Within the section "seatProvider" of your model .mdl you can enter a reference for the meshes that should be used for your crew (parameter "crewModels")
Code
seatProvider = {
crewModels = { "characters/era_c_wom_02.mdl", },
drivingLicense = "BUS",
seats = {
This examples references to a vanilla "normal" person but this should be also possible with individual/repainted person .mdls (if you want). I think dview has done this with some of his mods.
Be aware: At least for me the exchanged driver .mdl is not shown in the model editor, but it works in game.