I had the same problem as soon as I came out to Germany but I had just done my IMCr in the UK... The instructor checking me out at the club covered every instrument with post-its so that he could see the airspeed and altitude only, but I couldn't... this included the RPM...
I did 30 minutes of circuits like this, and he told me fly by feel and sound...
Although I would not recommend doing this while solo, make sure you have a good instructor with you... what really scared me is that my flying was better than when I could see the instruments... And this was backed up by a little GPS thing on the plane that you can plug a USB into view on Google Earth.