It is definitely possible - I've been in your shoes and done it. Transferred an H1 from an existing employer to a startup run by my biz partner (who also had a majority share). We hadn't raised any $$ when the transfer happened, though we closed an angel round a month after the transfer happened.

Things may have changed since 07 (funding requirements, etc). IANAL, though - you definitely want a good immigration lawyer who's familiar with this stuff.