does he still like the distortion from this amp if he uses its line out? if he does, you could get a loop box (switches a loop in and out of the chain) and put it in the loop of that. eg.

little amp (in then line out)
--------- | -------- /
guitar>Loop Box>other distortions, rest of pedalboard>amp

something like that should work

twon

I suspect that the "15-watt Fender amp" is either a "Pro Jr." or a "Blues Jr", st least those are the (2) 15-watters that Fender makes that have a decent OD to them. Certainly better than the Valvestates' distortion. I know that on at least the "Pro Jr"s chassis there is NO line output, even if you wanted to use that. But that's OK, because line outs on any amp usually sound like crap anyway. You need to tap the sound at the speaker output to get the "real" tone from the tubes. You do this by getting a quality DI box like a Radial, or a dedicated power attenuator like a THD Hotplate. You drive that little Fender's speaker output (it's on the underside of the chassis-real awkward) into a box designed for speaker levels, THEN you take the output of that into the rest of your rig, terminating into the Valvestate. I have used a Pro Jr like that many times, in fact that's my favorite way (through a Hotplate). I avoid using the internal speaker at all times because the positioning of it right up by all the tubes tends to vibrate them to the point of being microphonic and super-noisey. Rock on, baby!