The idea of stepping down the volume before the loop (with a volume pedal or resistors) will help the effect from being overloaded with signal, but consider what's going to happen *after* the effect. You need to bring that level back up to normal (very hot) levels for the PI again. I doubt that pedal will be capable of doing so. This means say goodbye to some of your PI distortion, which is critical for that amp to get the overdrive sound you're getting.
Try the pedal in front of the amp, as several people here have recommended. I as well have used delay pedals in front of amps and liked the result; I actually prefer it. You may have to turn the effect mix on the pedal down (I use 10%-20% mix), but the sound is actually quite nice. I find it more natural, warmer and broader, more reactive, than having a "super clean sounding delay" in the loop.
Other than that, if you are absolutely insistent on keeping the delay "clean", slaving as Ralph mentioned is the only other alternative that's going to work for your tastes. So before you say "screw it" and sell the VM because its loop isn't for you, at least try the pedal in front of the amp and actually give it a chance, try different settings etc. Because I honestly doubt the Stiletto is going to work out for you. Don't ask me how I know; I just do.