How to? Parallel processing w/plugin that lacks mix control?

The way you are doing it is how parallel processing was done when it was invented & is the reason for the “parallel” in the name - you have 2 signal paths running in parallel with each other. The config you have isn’t intrinsically more complicated than the mix knob method. In both cases you need set 2 controls to get what you want. For the mix method it is the mix control and the overall level. For the parallel method you are setting the individual levels of each of the 2 tracks. Additionally the true parallel method offers you more flexibility. For example you could EQ the compressed channel so you were compressing only the lows. I wouldn’t spend much effort on trying to fix something that isn’t broke.

As Grim says you could route it a bit more simply, but as is works fine.