Jack chuckles. "Well, yeah, done that too, in the past. Easy way to make a buck or two, when needed!"
And yes, of course he can manage to unzip those jeans without hurting anything, even whilst being kissed - and kissing back enthusiastically. He's had a lot of practice at such things. He's one of those guys who can unhook a bra with one hand whilst kissing too, not that that's going to come into practice in this encounter. (Well, unless they get some gender-bending going on too, that is!)
He gets the zip open with ease and slips his hand inside, getting his weight onto one knee beside Spike to allow plenty of room for such manoeuvres.