Believe or not, it happens. Technically it is possible because you fill out same I129 form and you check the item of change of employer (assuming you are still working now). On the USCIS webpage they explicitly said they will still process people who are changing employer, didnot say anything about whether your current H1B is against quota or not. Good luck! Had I done this earlier this year I would not lose a very good job offer. Later on I heard from other people who did so under the same circumstances and he was transfered to Eli Lilly from academic post doc position while the quota was gone.