I've found references to this on various other sites, but have no first hand knowledge of it.
"high capacity mag for the 9mm Hi-Point rifle are produced by Drummy. They are built exactly like Drum magazines for UZI's, MAC 11's, and GLOCK machine pistols. To get a 72 round Drum mag from Drummy, you must send a Suomi drum magazine and a 10 round mag that works well in your rifle. Drummy does all the drum modifications required and tests each drum produced to insure it functions in a stock Hi-Point 995.
You can contact Drummy at: PO BOX 1695, INDEPENDENCE, Mo. 64055. Suomi drums are available through SHOT-GUN- NEWS and on the Web for approximately $25.00. Drummy communicates through the US mail only. Once you have made contact, Drummy will give you his shop phone number."
Again, I have seen references to this, but have not heard of anyone actually having one built or how it ran.
Here is an old thread discussing the possibility: