Well there was a thread about somebody stating that he had a double pop in some skill while back, don't remember what skill it was. Well if the skill, which generally pops in 1-2 weeks, had a double pop, then I wouldn't argue that it's impossible. But if the skill, which generally pops in 2-3 weeks, had a double pop, I don't think it's possible...
If it's 2-3 weeks to get a pop, then the level should increase by 0.5 at its best (considering that a skill pops when it goes to the next integer). But to have a double pop, then the level must increase by at least 1.1 (considering that the current skill is say...5.99999). I doubt this is possible under any circumstances...(again, this is for skills which take 2-3 weeks to pop).