There's always the approach where you just "play what you feel like playing..."
I really only use the chords as kind of guidelines, so if I was playing a piece in Cmin and came across an F7 chord, I wouldn't just run up my F Mixolydian scale- I would just play what came to my head, and try to eventually land on one of the major notes of chord (F, A, C, Eb).
Every other note can also be used, you just have to know how to use it, which, I suppose, takes practice. Also, try listening to
everything. I found I really cool way to use the b2 note by listening to an Brittany Spears tune.
Or, whenever you get stuck, just do some chromatic thing up to one of the chord tones....
....the end of the keyboard solo in Steely Dan's "Black Cow" is what I'm talking about....
...meh, I don't think I'm making much sense to myself....
~Kal