Short version? No, not the way you describe.

Long version? Yes kinda, but it'll cost money.

Start account C. Do NOT link it to anyone. Transfer the mage to account C. Now you can powerlevel A and B in group with mage on C.

That's the only way I can think of that you can have a new account getting triple xp and boostable with only 3 accounts.

edit:
Thought of another way, if you have a buddy who wants to get some RAF benefits, have him invite you and create account C with it. Then the mage can boost the C account and your buddy.