For starters, it can help to get a server with fewer players than the map size... say alter your filter for large maps only (64 players), and try to find one that maxes at 32 (don't pick one playing Wake... as it can easily be the only large map in rotation... I think that's the only version of the Wake map). For a lot of things, this will help (even if looking for Karkand... find a large-map Kark server that tops at 30-40 players)... the rounds last longer. It's hard to find a 16 player server running a large map though... and sometimes it takes forever... 8 vs 8, and you may not meet the enemy often.
I got mine tonight on a 64-player map of Dragon Valley, with about 30-some players (it was a 64 player server, but it just didn't fill up). I think I could've gotten vet the way I was going, as I didn't start going exclusively C4 kills at first. I was C4'ing the flags.
1) Plant a load of C4 on the base of the flag (I wasn't able to get consistent with it, but if you hit the base right, the C4 will dissapear into it, just like the grill of a jeep). 2) Hide... hide well. I was hiding completely out of sight. 3) Watch the mini-map and wait. Blow the C4 the instant the flag turns neutral. 4) Re-take the flag, and hopefully repeat.
Helps to have a commander willing to drop supply crates for you. If there's plenty of squad room, create a squad so you're squad leader and can request supply drops (Caps Lock for command screen, r-click on the map and hit "Supply". This creates a yellow supply crate icon on the map which the commander can click on with two options, "Accept" and "Reject". Obviously don't drop the crate *right* on the flag... as you'll blow it up your next detonation... and if they're trying to take that flag vigorously, you could resupply 2-3 times before the crate dissapears).
Like I said, I didn't start the round with this tactic, and there were a good 60-75 tickets left when I got it. I probably had about 20 C4 kills. All of them were from flag pops except 2... early in the round I caught a Cobra landing to cap a flag (why he landed, rather than hovered I have no clue), so just ran up, C4'd, and I *think* he got the idea just as I was out of range, because he started to take off and spin around... too late though. The second came right after a flag pop... I had C4'd the flag, then gone back to the crate to fill up again before I hid. When I blew the flag there was still an enemy APC (or anti-air, can't remember) around, and I got up on them without them noticing.
I was hiding completely out of sight... a lot of the flags on Dragon Valley have buildings nearby, with a couple of them having rooms and hallways you can hide in (I was only discovered in those places maybe 2 times in the round, with a good 8-10 successful flag-bombings (killing 1-3 per shot). You may be able to get more points if you get where you can see the flag. It's riskier, and you're more likely to be shot (if they commander spots you, they may look in that direction, if you're visible, they're gonna shoot, if not, they may wait to take the flag, then come after you... of course you've killed them by that point). But if you could see the flag, you can pop them before they take it, and get Flag Defend points too. I'd rather get out of sight though... when it turns neutral, you *know* they're in flag range, so they're in C4 range (dead as hell if they're infantry... probably so even if in a vehicle, given they're right on it), and the few times I tried to watch the flag, they got me before I got them.
I wouldn't try this several rounds in a row... a couple of the guys started getting wise to this towards the end of the round, and came looking for me before hitting the flag. Another possibility is to save one pack to place near the entrance to your hide-out. The goal would be to put it in a place that will kill them if you trigger at the moment you first see them coming in, but won't kill you (because if you're triggering on the units capping the flag, you need to be alive to re-take it. I got 70 points that round, almost all from this tactic.