No, once a card is activated it is locked to the original receiver number essentially (as far as Bell is concerned) to that receiver, both in the inventory system and on the card itself.
If you have access to the card number though, you should be able to transfer it, then a new card will be sent to replace the (nonexisting) old card. You may be able to pull this off your profile on the Bell site.
If you get a good CSR and explain that the card is missing, and that a new card must be sent anyway, they may allow you to transfer the unit. Worst case, call up and say you have a couple of cards and see if they will tell you which one should be in that reciever LOL.