Bare minimums would be to keep the scan of the instruments going, not to fix on only one of them.
If you don't have an AI, the only thing that works is to keep the compass or DG (if you have) pointing in the same direction at the same time as the speed and altimeter should be "glued" on the respective values. (unless of course you need to get to MSA)
I had a not so pleasant experience doing a long ferry over water (lucky enough). I flew through a front I was not briefed about by the Met-office, that came up beyond PNR, and nowhere to land....!
I had my IF rating, the helicopter had an AI, DG and an old GPS. I went back to what my instrument instructor told me "pitch, bank, power" (altimeter for pitch, DG for bank and airspeed for power) and kept the scan going until a popped back out again after about 10 minutes in the ****.. (I had radio comms with destination, and knew the weather was good there, and no terrain between, so I fortunately didn't have to climb to get to MSA) By far the longest 10 minutes of my career to date!
As said above, the best is to avoid IIMC altoghter
