As someone posted earlier in the thread, I'd much prefer a time limit rather than banning communication. Something like this (maybe with tweaked numbers):
In each round of alliance member selection, Alliance Captains must invite a team within 70 seconds, minus 5 seconds for each invitation accepted in the round.
The numbers might need to be changed for communication on the 7th/8th alliances 2nd pick.
EDIT: Realized declines do happen
and if a mid-seed gets a decline then the timing would be disadvantageous compared to if a 1st seed got a decline. Harder to make fair than I thought.