Salvaging sponge tyres - by truing & capping?

[WillyChang]

This recently arrived, to complete another holy trinity...

The tyres are a little worn though, about 1-2mm off 'new' thickness.

And more annoyingly, they aren't equal L-R either.

Was thinking...

1) how does one 'clamp' these front tyres to true them equal?

--- without leaving any marks on the wheel etc etc

2) anyone tried 'capping' succesfully yet?