The quorum requirement is a senate rule, not an assembly rule, and does indeed apply only to budget bills.
The assembly and senate judiciary committees could meet jointly and pass the bill. Without a Chuck Chvala type to block a pulling motion, the bill could be withdrawn from committee the next day, voted on the floor of the assembly in the morning, messaged to the senate in the afternoon, and be on Walker's desk by end of day or first thing the next day. It could happen that fast if they wanted it to. All that would need to be done would be for the two Fitzgerald's to get their troops to agree to no amendments.
The media would howl, but the Republicans could say that they had to do something while the Democrats were away, and this was a bill that had been voted upon several times over the years and needed to be taken care of. Even the Journal Sentinel ran an editorial the other day suggesting concealed carry be passed (albeit at the same time creating new gun restrictions).
I really think someone should light a fire under the Republicans. Call Jordan Austin at the NRA.