I've always used the spin halyard attached to the bridle. I've done it for years and never had it go wrong.
With the mast down and shrouds attached properly, run the spin halyard to one of the bridle tangs on a hull. Temporarily attach the forestay somewhere convenient on the mast (I use the gooseneck). Now lift the mast to vertical and, once there, take up all the spin halyard slack and cleat it. Your mast will stay up while you step off the tramp and rig the forestay properly.
That's the way I've been doing it for years as well, I rarely have any 'helpers' available when I'm rigging up at home.
The only difference is, I always step the mast while the boat is still tied down on the trailer, and trailer hooked to truck, so I tie the halyard to the mast support post on the front of the trailer. I also use one of those $10 Walmart floating seat cushions between the mast and the rear beam, while I'm putting the mast step pin in.
Then just lift it up and push forward (be aware of which way the wind is blowing!) and pull the halyard very tight, step down and tie off the forestay to the bridals, then release the spin halyard and UNTIE IT FROM THE TRAILOR! It gets pretty funny when you try to pull the boat off the trailor with the halyard still tied to it...or so I have heard.
