Re:PSYN as a VSTi please !
There's already a way to do this. It's been a while since I tried this, so the finer details of the process escape me at the moment. It involves copying the .dll and all of the PSYN subfolders over to your VST folder and re-scanning it. You can't have two instances of PSYN sharing the same I.D., so you'll need to unregister the DXi install using AnalogX DXMan, TenCrazy's Window's Shell Extensions, or some other method.
I also recall having both the DXi and "VSTi" running simultaneously, with two slightly different version numbers of PSYN II. One was the updated version from Project5 (PSYN -> PSYNII), and the other came with the Sonar installation. There was only a minimal point version difference between the two .dlls, but that was enough to give each one a unique identity (as far as the installation was concerned). The feature set appeared to be identical between the two.