FM-up and FM-down.
One transmitter on 432. Multiple receivers on 2M -- maybe 8 would be cool each set to a different frequency, each with a distinct PL tone for access.
On the satellite each of the receiver ports is mixed together at audio frequencies and output on the downlink. The volume of the mix is determined by S-meters and the louder signals on the uplink are mixed in at lower volume.. The more power you use, the quieter you sound. This is so while the big guns are chatting away at very quiet, low audio, the guy with the HT has a chance to break in and boom over everyone.
The idea here is to make a satellite where the HT's have a chance. Also, multiple receivers make the system usable over areas where pirates are transmitting on the uplink channel. (Provided pirates aren't on ALL the uplink channels.)