Both the R44 and 22 are on the approved model list for the JPI EDM700, and the FAA flight manual update exists, and it is STC'd, so it is theoretically possible to fit this instrument to Robinsons. You may have a job convincing your local CAA man it is a justifiable mod but it is possible. It would probably be easier in the States. It would be even more difficult to convince him that a vernier was justified.
As B73 says, Robbies as supplied should not be leaned on a whim.
I'd love to have a go in a modified, properly certificated one though. Are you up for it H-R?