I know of no easy answers on this but here are a few thoughts:
-Small boats like this often raise their mainsails while hung off a bowline at a dock- bow into the wind, and then sail off from there.
-If you can't do that and need to raise the mainsail underway, then you really need to figure out how to raise the sail from the cockpit while steering with the tiller between your knees.
-There are things that make raising the mainsail single-handed much easier. If you have a bolt rope that goes into a groove in the mast, then you might want to buy a 'pre-feeder' like the Holt feeder seen here at the bottom of the page- http://www.apsltd.com/c-1061-headsai...refeeders.aspx
Or better yet, the Harken part #947 Prefeeder seen here Harken Hardware Catalog
This will allow you to raise the sail without having to be at the mast to feed it into the luff groove.
Alternately, have slugs installed on your main, if you do not have them already.
There are tricks to raising the mainsail underway, but the can be risky in shifty-gusty conditions. The consist of sheeting the boom close to amidships and start raising the mainsail while facing roughly into the wind. Most boats will reach off a little and then round up into the wind, tack through and do the same on the other tack. That is called short tack and if you allow the boat to short tack, you can partially raise the mainsail every time you pass through the wind, until it is all the way up.