In reply to dread-i:
Yes, there's a bus which goes up the A487 from Mach, so NBR could leave his car there in the big public car park in the middle of town, or find a free option, eg behind the Plas, and then hop on the bus. That's no good for the north side of the mountain though, if they're set on something like Cyfrwy arete or camping at Llyn y Gadair in particular they'd have to walk over the mountain.
One good option with free parking might be to park at the layby at the top of the Tal-y-llyn pass and then walk up the north east ridge of Gau Graig and then Mynydd Moel. There's plenty of discreet places to camp if you examine the map.