A slight spin on the overlay approaches already mentioned is where the crew 'create' FMS waypoints commensurate with the desired approach and fly them in sequence, with reference to the primary aid.
For example, a straight in VOR could easily be coded by the crew and flown using the FMS - but to be legal the aircraft must be navigated by the required navaid - probably goes without saying it can be fraught to do it this way, but its an option if you ever need it I suppose.