In the 1-minute demo below, you'll see the EVO being set on top of and removed from the Touchstone, charging and not charging accordingly.
Full details on how this was done aren't given, but the modder does say that it involved taking the EVO apart and soldering the connections. [UPDATE: Q&A with the HTC EVO Touchstone modder]
Amazon sells the Touchstone for $24 and a Palm Touchstone Kit for $46 that includes the charging dock and the Pre's back cover if anyone wants to do some inductive charging experiments while we wait for the original modder to put out instructions.
And if you get it working and care to write up a tutorial so others can do it too, you know where to send it.
UPDATE: Tutorial now available!