If I was IFR in IMC then I would definitely stick with the RIS and overfly the ATZ at 2400ft.
I recall a flight several years ago when I had a RIS from Thames Radar (before they got too busy...), VFR but in poor visibility. Passing North over the QE2 bridge the controller suggested calling Stapleford due to the potential for IFR training traffic OCAS. It may just have been a means to politely get rid of me, but I have called Stapleford ever since, or routed South around the ATZ. I admit that there isn't much the FISO can do except say "it's busy, keep a good lookout".