Good advice from Chris above.
I had trouble streching sprue before also. It takes some practice, here's what I've found;
To soften/melt the sprue I roll it above a candle so that it gets evenly heated. I start with it quite a distance from the candles flame so I don't burn it. Slowly move it closer to the flame as required. Continue to roll the sprue above the heat source until it melts enough that it bends or (for want of a better word) gets "limp". :-[ Nows it's ready to be streched. Pull the two ends apart at a constant speed. With practice you can vary the thickness with speed.
Another option for antenna wire, is to visit a local fishing supply store. I often use a product called "Spider Thread". I like it because it is kind of "stretchy", takes paint not to bad, and really adheres well with CA. Great stuff if you can find it.
http://ecx.images-amazon.com/images/I/31NDEF39QKL._SL500_AA300_.jpg[img]
Nylon thread can also be used. Tighten it up with a hot blade the same way Chris describes above.
Hope this helps.