Using a pipe stat and return loop pipe on the DHW draw-off back to the
cylinder, a secondary circulation loop can be added very easily using the
same pump. The return pipe only need be very small bore plastic to thread
through joist, etc, just like cable.

In fact, you would want it very thin, as you don't want the secondary flow
to reduce the outlet pressure. Obviously, you can also balance it down with
some sort of valve, too.

I can't help thinking that a single impellor shower pump would be too noisy
for a secondary loop installation, though. Some might not like the low flow
rate and high pressure drop when no outlets are open.

Christian.