the real best plan .. take out the BB put some corks in the chainstay tubes and fill the space where the KS will squeeze with like epoxy putty
then the tube wont crush.. other than that use glue and a sheet of rubber,, and glue the rubber to the frame and KS
to the rubber , it will want to rotate .. towards the spokes is not good..
You dont have to leave the legs as is full length , But I see many do. they are marked matching BB Height..
the weight on the legs will have them spread out, some, so dont cut too short ..
they the swiss company make replaceable rubber Feet to go on the ends to not scratch mark floors
they also make a plate for the frame .. it is held on by the bolt that holds the tip of the rear mudguard on, but it is not universal ..