I am making the following assumptions:
1) You only need to repeat those commands that are for devices at the end of that run.
2) You can't, or don't want to, install a booster/coupler/repeater device.
In that case, using an RR501 is a good way to get the RF signal into that "isolated" portion of the house. The only question is how to get the RF signal to the RR501.
Since the CM15A can transmit RF, you can create macros to do it. I would recommend putting the RR501 and any devices you need to control on that leg onto a HouseCode that is different from your regular one.
Then create macros to transmit the codes.
For example, if C8 is the light right now, move it over to D8, switch the RR501 to "D", anc create a "C8 On" macro that send an RF command to "D8 On."
That way, you can still use remotes, sensors, and other stuff that can talk to the CM15A, with no fear of duplicating commands.