I'm not sure you can, although ISTBC. Looking at the partner T&C's on the VS site is does say
Discounted rates ineligible for Flying Club miles include rentals involving free, complimentary, non-commissionable travel industry rate rentals and tour rate products (rentals as a part of a holiday package), rentals under corporate agreements that prohibit the awarding of frequent flyer miles, insurance replacement and body shop rentals.
Also, from personal experience, we booked a Dollar rent through FC using some of our CDC allowance and it has taken A LOT of discussions for them to accept that the rental did qualify for miles.
I guess it can't hurt to send your claim form off, all the can do is say no!
Neil