An interesting topic that Is really quite serious.
To me an Enroute IR just wouldn't work in helicopters. As has been previously mentioned to do IFR in IMC requires proper training and a capable approved machine. It's a different story in aeroplanes because they are naturally stable platforms compared to helicopters. And why would you want to do IFR in VMC? Just go VFR!
It's all very well getting VFR on top but if it's a broken or overcast day how would you get back down? You need to have proper cloud break procedures (App Aid/offshore let down) that would need to conform to MSA, you'd want radalt to be safe and radar to see what's ahead. Then you're in the territory of an IFR machine (£££). Although FAA machines can do IFR with single engine Robbins etc there's a reason they stay out of cloud.
lZ