Penalty free 401(k) withdrawals at 55 years old

Could not find this topic addressed previously...but thought it might be of interest or solved before...

Corporate early retirement allows withdrawing from taxable 401(k) at 55 instead of 59-1/2 years...

I am looking to optimize some ROTH conversions, but results seem to be affected adversely...Pralana seems to be limiting conversions in early years, with larger conversions at 59-1/2...

Any suggestions on the best way to get this to work in the model?