There are several solutions to this
- Radio call (Influence)
Pay 500 influence on green zone and increase by 100% with each dificulty for a max of 2500 at lethal
- Radio Call (Daybreak)
Pay 1,250 prestige points per survivor.
After the radio call the screen could go black and send you to a menu, similar to the menu when joining another match or a menu like when you character left the boundaries of the game with a picture and a name of all legacy survivors for the players to chose
This should have a cooldown option, and a long one to prevent players from calling entire communties and not trying new survivors.
Idea proposed by Marc T.T. & Leonardo David Tufiño Zuñiga