you guys have completely confused the situation.
there are 3 method i now to stiffen the rear subframe.
1. Alu Locking Collars..
these are available in complete rings or C shape. complete ring collars need to have the subframe droped to fit, but with the C shaped you can just loosen the mounts and prey it apart just enough to slit on c collar in.
Aslo with these you dont remove your original bushing. thses work by compressing your orginal bushing rubber given you the same effect of replacing the orginal bushing with stiff items.
2. Pineapples
These are very simlar to the lockng in which the slide in between or under the subframe depending on your setup grip or drift. they are also made of polyeruathne. not sure if the come in c shape. but if not will need to drop the sub frame to fit between. Also with these you dont remove your original subframe bushing. these work by changing your subframe angle and height which can give you more grip or loose grip depending on your requirements. these pineapple dont actually sqeeze the orginal rubber bushings at all.
3. replacing subframe bushings for stiffer items i.e. poly bushes.
This involve removing the original rubber bushing, which requires the subframe to be totally removed and haveing the old bushed pressed out.
if pressing is not a option.they can be removed by buring the rubber off so the centre metal peice willfall off. then using a hacksaw to remove the metal ring that the old rubber are pressed in on. some hammer action wil be need to get the metalring out. then new poly bush get squeezed in.