If I read you correctly, you are proposing to put the XPCR wires under the same breaker screws that the dryer wires are currently using (as is shown in the XPCR manual).
If that is your intent, you should gain the results you want, but there are some problems that could arise: If the breaker only has one set of screws, that is considered "double-lugging," which is flagged by inspectors where I am. Also, the XPCR is being supplied by a high-amperage breaker, which may provide little or no protection for the XPCR wires.
The idea may be sound, but the execution is probably not.
Ditto on Jeff's repeater (said the guy who replaced his XPCR with Jeff's XTB-IIR).
Steve