you dont need to hold down ~ to tweak. there is a toggle check box to turn on tweak mode. hold W + left click to check that. what you are asking for is best done in sculpting applications but you can somewhat mimic it by having soft selection("b" toggles soft selection) on and in face selection mode. also dont use face…
the same tilde tweak is also in maya 2008 ext 2 otherwise jes turn on the tweak option in yer transform tools options. ( which might also be preferable to holding down the tilde when in a heavy tweak sculpt session ) for brush like behavior remember to use the b hot key to enter and set soft fall-off. fer quick zbrush like…
Maya 2009 has a "tweak" tool in it now where if you go into component mode, select a vert, edge, or face and hold the ~ key you can tweak verts, edges and faces around. It works best if when you are holding the ~ key you move the components with your middle mouse button instead of left clicking and moving them.