I have, in fact, used my emergency tiller in anger.
It worked. I managed to get the boat back into the slip with the e-tiller. BUT: the rudder cable broke pretty close to the entrance to the harbor. I needed to steer with the e-tiller for all of 15-20 min or so. (Of course, we were also next to rocks and a beach which made getting the e-tiller working much more important) It was hard to steer at basically idle speeds - the wheel was in the way and I couldn't remove it due to a jammed nut (now fixed). Had to use legstrength in addition to arms to steer. Absolutely no way could I have been under full sail with it. (On a Catalina 30, so not all that big of a boat either).
With that experience behind me, I've got some ideas on what I would do if I needed it for a long distance and not next to a lee shore.
1. I'd try to fix the wheel first. I've got dyneema lifelines I could cannibalize to replace the cables. (For a bluewater boat, I think a spare set of cables on a cable-steered boat would be a good idea to have on board)
2. I'd remove the pedestal, and lengthen the tiller. (Lash something to it.. boathook, whiskerpole, gaff, stanchion, etc...)
3. As mentioned before, lines from winches to the tiller, I don't think that'd work all that well on a fin keeled boat under sail. Bit a full keeler that tracks like on rails it would work fine.