not sure what to call it, but you could have a flag that cannot be dropped, and gives the carrier 10 or 15 secs to come into contact with another tank, if it does, this tank now has 10 secs to get rid of it, etc etc, and if your time runs out, *boom*
alternativly (my original idea) was to make it so that if u get the flag, you will die, but if another tank is close to you, they will also die, so you can still gain points, but if u dont make it to a tnak, you die, loosing points.
An idea for a flag
New flag
Sounds a bit like the "Kill or be Killed" flag.
http://www.bzflag.org/wiki/FlagList
http://www.bzflag.org/wiki/FlagList