My question is this: Is it theoretically possible, even if extremely unlikely, that a setup like this can solve a block?
No ... even with my 12GH/s, i don't have solve a block since it has started.
I push 50% of time on pool and 50% on solo mining (not to find but to help transaction fluidity).
But that just means you haven't been lucky enough to find a block going solo? Doesn't mean you won't be able to.
There's every chance for a new solo miner to switch their HW on and find a block straight away, unlikely, but possible. Just depends on how lucky you are.