Single handing with a big spinn is quite doable.
It the raising/deploying part that can lead to problems ... and once youve mastered the raising, etc. its actually quite easy. I say that with tongue in cheek as you need a LOT of spinn. experience to do this; but, if you raise the kite very often and at most opportunities it gets easier and easier.
If you have a LARGE spinnaker crane that keeps the top swivel AWAY from 'eating' the spinn cloth, you can simply deploy/douse the spinn in the shadow of the genoa (with sheets 'mostly' tight' or pre-marked sheets, etc.) and furl the genoa in/out as needed.
Note: if your top swivel is in 'close' proximity to the spinn cloth, choose another method as you dont want to as a single hander need to go up the mast all by yourself with a knife in your teeth to slash away a spinnaker that has been 'eaten' by a furlers top swivel.
If you have 'clean' rigging - no hooks, sharp edges, 'catches' with which to snag/tear ripstop ... if you need to douse the spinn in moderate or less conditions, simply go through the eye of the wind and heave-to which will 'stick' the spinn to the windward side of the genoa/main. While hove-to or forereaching, then you go forward release the halyard and PULL the spinn down from the windward side of the main/genoa.
Obviously, your not going to singlehandedly fly a spinn in 'heavy' or 'boisterous' conditions.
Without an autopilot as the OP suggests. ? If yes RESPECT!