I've been given a Domme's left hand before. She would tell me what she wanted done and I would humbly explain what "my" left hand would be doing. She allowed me to use two fingers as my tongue too.
Granted, it's not the same, and it takes a lot of typing, but when my Domme is far off and I have no other recourse... *shrug* It satisfied her. That's all that mattered.
I've had to provide a LOT of erotic fiction while Dommes have been on trips or what not. Sometimes they would give me a specific topic. Other times I've been required to keep a plug in my rear and masturbate every hour (even while at work!) and report as to how I brought myself off, what I was fantasizing about, and where I did it.
And then there are photos... I've had to tie myself up or bind myself while the camera's timer ran so I was in this pose and then that pose. Then I'd send the photos to her e-mail so she knew that I actually did it.