Looks like both my ideas aren't going to work.
When I finally thought about it, I realized the charge timer can only go up to "59" before to rolls over to 1:00...so that won't work.
I messed with the ambient temperature today and got nowhere. There is something seriously messed up with it. It read 61 when i started. After messing with some messages, it suddenly dropped to 41. But I don't think it had anything to do with me. I messed with it for another 1/2 hour and it just naturally went up to 43. I gave up and headed home. I went three miles on the highway, and I watched it count up 43,45,48,50, to 53 in a matter of about 45 seconds right after I got off the highway.
Anyway, I haven't given up totally on the temp sensor display, but I don't see any other messages I could "hijack" to display the SOC on the dash...with the exception of the range. But that message gets transmitted quite often so it might be hard to override cleanly.