If I'm reading your post correctly, I'm guessing you're manually keyframing your image frame-by-frame via the Frame & Fit Editor? If so, I will be sure to add your suggestion about being able to adjust your object's perspective when tracking to the motion tracking/feature request write up.
That’s exactly the process iI tried to describe, you got it.
Most of LumaFusion users use keyframing as a simple motion tracking function. Manipulating perspective may be simple enough (unlocking size relationship between each object side).