THe only GA GPS that I know of that you can enter a hold at any waypoint is the Garmin GNS 480, but then it isn't really a Garmin. It is the "ant pants" tho. Garmin bought the company that made it then eventually took it off the market. It was/is far better than any of the Garmin developed GPS's.
Not only can you build a hold, the GNS 480 when connected via GPSS to any autopilot will fly the correct entry and then the hold. If you are hand flying it tells you what type of entry to carry out.