I think you'll have to take the undertray under the undertray off so to speak. The panel that sits below the fuel tank with the gear and brake cables running across it. Then you'll have access to the edge of the fibreglass from beneath the car and will be able to lay some (supported) fibregalss with resin and fix a captive bolt in it in the correct position. Not a big job but messy and a lot of work to get in a position to be able to make a decent repair.
So, Jack up the car, remove wheels and disconnect brake lines from calipers, also from the engine compartment remove the gear cable locator bolt. Enure you don't lose the bushes that dampen the cables from the gearbox.
To remove the panel first remove any cables across it from their fixings. Then take out the five 13mm bolts out closest to the passenger compartment, four 17mm nut and bolts that pin the wishbone mounts to the panel (two 17mm spanners required), the two 10mm that connect the engine mount and the two 13mm nut and bolts in the rear corners.
I only know all this because I'm about to remove this panel myself to put in a ProAlloy fuel tank and I've cribbed from SteveA's topic here =
http://www.vx220.org...loy +fuel +tank