Headliner conversion

I just read redfish's thread about his headliner woes and have a question and I didn't want to jack his thread. Has anyone ever heard of anyone converting from bow to board headliner? I read something about a company that was doing that for the new Dynacorn mustang bodies. It was supposed to give like 3" more headroom. Seems like a great idea, but it was outragously expensive and only for the mustang. My old Galaxie's headliner has a few small tears and I have been thinking about trying it myself. They started by laying fiberglass on the outside of the roof and splitting down the middle both ways to make it fit. Sound crazy or do-able?