I've got an uprated engine mount under the battery and dogbone mount, that thing was used in the Cliocup and rally.
I've also got an extra gearbox mount on the subframe from a 19 16V.
I still get the feeling that it should be tighter, but that would be just too uncomfortable as you wouldn't even be able to see anything in the rearview mirror.
Those Cliocup mounts are for sale over here for about €110,- for the dogbone and around €70,- for the under battery mount.
The mounts are still available from Renaultsport, so maybe your dealer can order them for you?