Unfortunately the IRS and the FAA have different views, so it gets convoluted. Typically, however without full details, you may fly anybody as long as there is not compensation to LLC1. Parent, affiliate, subsidiary companies are in some cases allowed to reimburse for expenses however that is a bit more in depth and kind of requires knowing more about the story. Separate or non affiliate companies may share operational expenses either under a time share, or dry lease - however again there are considerations. If this is going to be a normal thing and the boss wants so move expenses between two separate companies a simple time share agreement is probably what you want. A wet lease generally requires an operating certificate and under a dry lease agreement, you as a pilot for LLC1 cannot fly for LLC2 as LLC2 in a dry lease must maintain operational control. If you want to play the game of "time off from LLC1 and Contracted by LLC2" go ahead, but, if it looks and smells like LLC1 still has OC by placing you on the aircraft - it won't fly.