That's what I do. I used to use Opus for the dumbest stuff, writing commits and such, but now that' all subagent business that run on Sonnet (or even Haiku sometimes). Same for running tests, executing services, docker etc. All Sonnet subagents. Positive side effect: my Opus allotment lasts a lot longer.

I’m just sitting here on my $20 subscription hoping one day we will get to use Opus

You can just get your own account right? Just pay out of pocket.