Don't have my DMG with me, but I'd say this falls under the pg 42 mindset... allow them to do it but at a cost. In this case the cost would be granting combat advantage, and/or -2 to attack due to the bulk of the crossbows.
Alternatively, I'd just rule that QuickDraw allows him to use the crossbow as Load: Free.
Alternatively, I'd just rule that QuickDraw allows him to use the crossbow as Load: Free.