Is it possible to bridge an odd number of amplifiers?

I’ve been in the car stereo business for a long time, and really should know this, but I’m stumped. I know many mono amps can be bridged in pairs, but I saw a guy at a car show who claimed that 3 of his 4 amps were pushing his one subwoofer, the 4th was a 4-channel for his mids and highs. Is it even possible to bridge 3 amps? I’ve never heard of this and it doesn’t really make sense, the guy had the work done for him & couldn’t explain much.