Sweet. That's basically what I was thinking too. Chris would put himself up for it if he found out that's what they needed (assuming he might find out from Pure if Sam told her at all?) so it's totally a possibility if you don't get anyone else who better fits the bill.

It could be Charmed logic, which finds loopholes for this stuff all the time, mixed with the requirements of SPN magic. That's really the best part of crossing these two fandoms in my opinion.