I agree with bookworm's common sense suggestion, but as thing stand, you can't selectively decide which aeroplanes you're providing a service to.
Working, as I do, in the unpredictable FIR environment, I know only too well that you can't legislate for freecallers or VFR flights that become IFR, but even in those circumstances the Part 1 requires you to establish separation by the quickest means possible etc. etc.
I'm not saying it's right, but let's face it, the Part 1 bears absolutely no resembance to what really goes on in Class G anyway. The worrying thing is, that if things had gone utterly pear-shaped and you welded two IFR RIS aeroplanes together, a good lawyer would drive a coach and horses through the 'they only wanted a RIS' argument.
This becomes a bigger problem at night, when everybody's IFR.