Forget about the boys in red, they don't matter.
Prohibitions are done by Orders In Council. An order could be issued by the government specifically de-prohibiting this firearm. It could be done on a friday and the gun would be unrestricted on Saturday morning. No house votes, no laws required, just a cabinet level decision, followed by issuing an Order in Council to the effect that the firearm is unrestricted.
They've already done this once under the liberals to de-prohibit the unrestricted valmets.
Here's the case I'm going to try and make:
Canadian gun owners are a loyal CPC constituency, more loyal than most others. Its a constituency with some serious concerns about the direction of the government on this file. There are some pushing for a more conservative or libertarian party, and there are others who see the status quo as being the only option an vote for other parties.
Point out that there are several NDP held ridings with widespread gun ownership (northern ontario, NWT, and etc...) These ridings are held on the strength of union ties, but they could be weakened if the NDP is seen as a threat to their right to hunt.
If the government took small, politically inexpensive steps to actively court this community, as they have with ethnic communities, it would bolster their vote total and could potentially deliver some ridings into CPC hands.
So, issue an OIC on the GSG5. Most people in the nation won't notice, it shouldn't be a prohib anyways. It costs the government nothing, it expends almost no political capital, but it is a symbol of being friendly with gun owners.
That's the tack I'm going to take (Will be at the convention in two weeks and I hope to drag Van Loan aside for a couple of minutes).