I use zip ties or cable ties, put it around the spring and tighten it bit by bit as you wind the spring by hand. Sometimes you can put the arbor in the spring and hook it over the pillar but with most of the mainspring outside of the movement, as you wind it up it will move into its proper position. The only thing you have to watch are the steel pegs put into the plates that stop the mainspring opening out into the gear train, if one of the coils is around one of these pegs it wont work for obvious reasons. Other than that you would be looking at buying a mainspring winder.
Paul.