I would be tempted to do this with a separate relay directly from the battery. However, you failed to mention the model year of your Mustang. So I can't directly recommed where to tie the pilot duty coil to.
If the 99-04 MY, consider using F2.34. There are tons of other places to tap for a low current pilot duty application. The CCRM is an easy spot. It really depends on what's easiest to get at and your preference.
If you would like a copy of the wiring diagrams, I may be able to help. PM if interested.