Sims 3 on Origin + Steam Overlay?

I know EA hates Steam, but I own TS3 through Origin because it was cheaper, heheh. I want to be able to access the Steam overlay while playing TS3 because 1) the Origin overlay doesn't seem to work and 2) having to alt+tab out every time I get a Steam message or need to use Chrome is annoying and often leads to the game screen going dark upon return for some reason. I've tried everything I know, but it never works - adding any of the TS3 executable files to Steam just either does a) nothing or b) opens an Origin window, neither of which are things I want to have happen in this situation.

I feel like this should be a simple thing, but it isn't, and I'm very disappointed. Does anybody have any possible idea how I would accomplish this?

Thanks in advance,

RL