Using bow spreader for raising mast? Bad idea?

Likely a bad idea. The bow spreader is very strong when being pulled at the correct angle with mast up. If you pull on it sideways like you would while raising the mast you will likely break the fittings. The wave has a pretty small light mast, shouldn't be too difficult to raise the old fashioned way.

I sail most of the time alone, I need way to raise mast alone. I thought I will raise mast up to at least half way by hand and then pull it up by line thru block attached to middle of bow spreader and end of forestay, then when mast up all the way I'm holding mast by that line may come ahead and connect forestay to bridle wires.

In that case you are probably better off getting a gin pole setup. The Mast Stepper III is designed specifically for the Wave.