I was messing around with an idea along these lines a while back, but at the time I wrote it off as something I'd need a more flexible signal path for. I don't have the patch anymore and, while I'm at work, away from my HD500, the best I can do is grab a screenshot from Edit which shows roughly what I would do. Equally, there's a danger you'll run into the DSP limit - you'll just have to give it a go and see what happens.

Pick whichever amp you want. Insert first delay followed by a modulation effect - that's your Delay 1 from the SR.

Insert delay 2 followed by a reverb - that'll be your delay 2 when in series.

Insert delay 3 (the one on the bottom) followed by a reverb - that'll be your delay 2 when parallel.

Set your delays 2 and 3 and reverbs 1 and 2 to all be activated by the same footswitch.

Set your expression pedal to control mix 0-100 for delay 2 and reverb 1.

Set your expression pedal to control mix 100-0 for delay 3 and reverb 2 - a simulation of the bleed control.

In the shot above, I've only dropped in FX types. I haven't picked a particular delay/mod/verb. It's as much thinking aloud as a practical solution. If I get a chance, though, I'll try it this evening and see what happens / whether it's actually possible.

And let me know if you try it in the meantime.