It sounds to me like the OP wanted to do just the opposite of what you're describing. Namely, given that a widget shows in the Dashboard, which overlays everthing else, how does one unattach it from the Dashboard floating display so that it can be used as a separate app in its own separate window, just like any normal app?
In any case, how can one do what I've just described.
As a case in point, I have the iStatPro widget that shows temperatures, etc. It's not really all that useful unless I can have it showing while I work on various apps. But as things stand, to use it now I have to interrupt what I'm doing and open the Dashboard, read the resuls in the widget, then close the Dashboard.
Incidentally, how can one begin dragging and then hit F12 on the Apple wireless keybaord, where you have to hold down the Fn key while pressing the F12 key to get an actual F12 instead of the volume-increase action? It would seem to take either gigantic hands to stretch between the two keys with the fingers of one hand while moving the mouse with the other.