If you join as a group, you will end up as BG leader 99% of the time, so you just need to move your guys to the same group and your set. Even if you end up in different groups, macros should still work unless you are using things like Party1, Party2, etc.. for targetting. The real reason you want them in the same grp is for buffs (since most just affect the group your in) - although in WotLK this won't be so much of an issue, since most buffs are being changed to become raid-wide.

Cheers,
S.