You can also do that by directing your HS router to use your relay as a bridge.
First add these lines to
torrc of your relay to set it up as a bridge:
ORPort <some port>
Exitpolicy reject *:*
Then configure the router that hosts your HS to use your bridge:
Bridge <bridge line of your relay>
There is no guarantee that rendezvous circuits will always go through the bridges with
UseBridges on. Tor may behave unexpectedly. Furthermore, an adversary could correlate your HS without effort since there are almost no hidden services behind a bridge.