May be you may consider another alternative which somewhat I was trying to first do and then switched to additional H1 option... However this was one of the method I had validated with the attorney and it might be practical.... However, you know your situation and the best is you should have a consultation with an attorney which will be worth it.
- Stay in your current company, work as a consultant to the new company through your current company till you get the EAD and 6 months from filing I485 and then just move to new company. New company can pay through existing company. You might give some little incentive to your current company for 6 months for taking care of payrolls which you can pay from double transfer costs of H1, etc and complicating your case. One thing is be careful not to complicate your case by jumping too much during your I-485 first 6 months till you do AC21.