I like the idea of her tying HIM up and playing with him instead.

I think this is a much more realistic scenario, actually. Angel is a big ol' masochist... suffering is part of his redemption. He might occassionally let Spike tie him up and flog him, but even with the whip in Spike's hand, Angel is still the one in charge. Buffy is the only person Angel would willingly submit to, because he worships her. I doubt she would ever let him have that same power over her, no matter how much she loves him. She's too much of a control freak.