All you need are three loops of 1/2"-5/8" line, tied with square knots or other secure knots. One about 6' tall, the other two about 8' tall. They can be used on any tapered spar--including many masts--as well.
As usual make sure there's a safety line besides your climbing line, you never want to fall when that "stuck" line decides to get unstuck!
Just a quick note as a climber... been climbing for many years (been lurking here for a while too), and have used prussics alot.
Please don't use a square knot for anything that holds your life... they are often called "death knots" in climbing, and are not suitable for any climbing situation. Double, or triple fisherman knots are what you want.
I also wouldn't suggest using prussics around the mast... it would likely work, but it wouldn't be safe.
Also never ever ascend a rope that is "stuck"... always use another line. The stuck line will give way.
Sorry to correct you Hellosailor... I normally think your pretty on track, but as I do alot of climbing, it is very simple for things to go bad. Every year, very experienced climbers die... very very experienced... from something small done wrong. If you have to use climbing methods to ascend the mast, please have someone who's been climbing for a while show you how to do it properly. Its your life, and I have seen many knots, or setups which look solid, and feel solid which would eventually drop you.
If you want, I can go more into how I would set up an ascender system, using prussics.
Just trying to watch out for your safety.