Yes I have thought about this, the top of the release valve does have a female pipe thread, but if I was going to plumb it back into the system or another tank, I would only do it if it made it safer than it is now.
HPCO is pre set to 350psi, release valve is 400psi. So assuming the (brand new) HPCO works, (It does as I have tested it) the discharge should never get above 350psi (+/- 5psi).
First job for the release valve is a second safety for if the HPCO fails.
Second job is to release pressure if static was to exceed 400psi.
I have the R1150 static down to 190psi now @ 20°C so the only reason the static would get over 400psi now is if the cascade was exposed to a fire.
In that scenario I would rather it blow off a bit of gas than keep building up.
To do it the way you mentioned totally safe, I think the release valve would have to be plumbed to a designated tank which would also have it's own release valve.
It must release to atmosphere under worst case scenario.