Is there a way of doing this keeping the main dimmer with the capability
of
dimming all lights?

I'm not sure if understand you correctly but clearly the relay coil
won't respond reliably to a dimmed input signal. But there's no reason
why it shouldn't switch a dimmed signal. Could you explain more fully?

What I meant is the relay solution is 1 but will not enable wall mounting
dimming. Is there solution that will.

Currently I think I am going to go slightly differently where I don't have 2
seperate curcuits but the 2nd set of lights which are located above the
projector screen can be isolated i.e. turned off when the projector is on or
light the other lights when the projector is off.

TO do this I need an X10 module to go in the light switch which supports
wall mounted dimmers and then an X10 module which acts as a 240v relay