If you guys have the time you should search pprune for DIY instrument approaches. 540, I too fly approaches (in a multi crew jet with Efis/twin fms etc) such as ndb or VOR/DME 'out of the box' or straight from the fms. This is legal. However, I monitor the raw data 'classic' navaids also during this time. Vnav gives me a kind of glideslope, as you talk about. However, this is not using a handheld gps!
Rnav approaches are becoming quite common nowadays. Good if you have the kit.