Boosting volume for solos for 2 amps without effects loops

Hi

This is my first post, so I hope somebody could help me out here?

I have a 2 amp set up - Marshall JTM60 with a 4x10 and extended 2x12 cab (this is for the vintage hard rock stuff); and also a Fender Blues Deluxe combo (for clean and slightly overdriven sounds).

The problem I have is that I want to use one boost pedal (currently a mxr micro amp) to boost solos. However, this means I cant use the effects loop on any of the amps as it's only one pedal. My pedal board will definitely not accommodate another mxr, that's for sure. So, you'll probably guess that it won't boost the signal as I want as I am using the drive channels on both amps, I.e. The boost will be before the preamp.

So, is there any way I could use just one pedal to boost the volume (not gain) on both amps (before the pre amp) without using the fx loops? Is there a pedal that could do this? It's basically like another master volume for both amps. Perhaps turning the gain down on the amps give more head room for a boost before preamp?

Just to point out, I use an A/B switch to select each amp, I don't ever use both amps on at the same time.

Hope someone can help?

Cheers.