Anyone attach an REL sub to Cary amp?

I like the way the REL subs connect into a system, with the signal being transmitted to the subwoofer via the speaker terminals on the amplifier rather than an output on the pre-amp. However, on most Cary tube amps there are only one pair of binding posts, or as in the case with my amp, a neutral and both an 8 and 4 ohm tap (I use the 4s). This would require having both the speaker cables and the sub cable connected to the same set of binding posts. They are multi-way binding posts that could easily accommodate the second set of wires for a sub, but I'm a little uneasy about doing it. Has anyone ever tried this with a Cary, or any other amp with a single set of posts for that matter?