On the Metro, the back of the rear subframe is located by a pair of U-shaped straps that loop around the hydragas units, which will support it in droop, whilst there are a pair of thick rubber packers between the body and the back of the subframe to take the weight. Obviously, without the hydragas units, the U-straps become redundant.
The standard Midas mod is to drill a pair of 5/16" (or 8mm) clearance holes on the top rear corners of the subframe and to locate the subframe through the boot floor using some damper top type rubber mountings, This is best explained by viewing the manual (the Gold convertible one can be seen on the MOC website -
http://midasownersclub.co.uk/downloads/ pages 37 to 39). You don't have to stick with the arrangement shown, the second rubber washer/bush could be underneath, between the subrame and the nut, so that only a penny washer and the bolt head show through the boot floor. The important thing is that two rubber washers/bushes are used on each so that shocks will be absorbed in both bump and droop, otherwise you will get much more noise coming through.