I am normally the one to initiate sex with my girlfriend (whenever I feel like it), and she's very receptive, so no troubles there. I always play a dominant role, even when she's on top, it's because I tell her to get on top. But, it's become a bit of a fantasy of mine to have her tackle me, pin me down, ride me and just generally take charge. "Asking" (telling) her to do this sort of nulls the fantasy because it's not spontaneous and of her own accord. So my question is: How do I go about getting my girlfriend to do this without asking (I obviously want to avoid trying to "negotiate desire" because we all know that doesn't happen)?