I created this application to help me brainstorm and experiment with exactly what you are trying to do - come up with alternative approaches/scales/arpeggios within the context of a key signature.
What it does is allows you to enter the fundamental mode - for example: Key sig. = C minor (Aeolian) - and it gives you the other modal scales that will be in lock-step with that key.
So using C minor as our starting point, you could:
Start on an Eb (nice chord tone) and run the Ionian mode/major scale/arpeggios and be confident that all the notes "belong"
Or start on G and run the Phrygian mode (minor scale patter with a b2) - and so on...
I KNOW THIS IS NOT THE ANSWER TO "HOW DO I USE THE MODES TO SOLO OR IMPROVISE?" - before the flame start... I understand that improvising and creating musically appealing parts has more to do with your ears and feel than anything else - but I have found that using this little toy sometime (hell, a lot of times) shows me some interval patterns or lines that are very interesting and useful.
http://www.mydigitalinnerchild.com/_...rator_v04.html
Try it - who knows? It may be great, it may suck. To me... it is just one of many different ways to approach being creative with music.