Blackhawk has the STRIKE mount, which is MOLLE compatible: you mount your SERPA holster of choice on it, in whatever orientation. So, you could mount it over your sternum, or appendix or wherever you want. I haven't used one, but it looks better than a many of the other options I've seen.
The only thing I could see that I would not like is that my SERPA holster kind of hangs off of my belt a ways, and I imagine it might have a tendency to flop around a bit when mounted to the chest, though I guess a good rig would mitigate that. It's something I've been looking to try out with a plate carrier, anyway.
They even have the quick disconnect system, which you could use to swap the holsterfrom a duty belt setup to an LBE.
edit: Blade tech also has something that might appeal to you:
http://www.blade-tech.com/Tactical-Chest-Rig-pr-919.html