Thanks for the post diverse. Im not a good soloist either and I had a hard time figuring out what to do. Here are things I do though. If Im playing lush chords I will play major and minor scales over them. I do scales in and out of the key Im playing in. It sounds like Im doing alot but Im not.
Let's say Im playing a 2-5 in Db and on the 5 I play.
Ab/Fmaj
I will play a F major scale up two or more octaves after I play the chord. It sounds nice.
Ab/Fmajor scale.
I also got a trick on that diminished thing something like what you explained but more dealing with chording. I think you mentioned it before.
One morning I woke up and got on the keyboard and start playing. Some how when I was sleep I understood the key to soloing. I was able to solo out of the blue. I felt God gave it to me. What I learned was placement of your fingers or hand position will allow you to solo. If you float your thumb over certain areas of the keyboard it will become easy to solo on the fly.
I think it has some what to do with placement of the thumb when playing scales. Usually all the other fingers fall in place behind it. Basically I will float my thumb around the C area or the G area. In actuality Im almost placing my thumb over every position for playing the first five notes of the major or minor scales.
No matter what key Im in I can solo from any position on the keyboard. I might play a lick in one position. If I know Im going to move up I will move my thumb up. If Im moving down I will move my thumb down.
If I was in Ab and I had my fingers over Ab, Bb, C, Db, Eb I can solo with any of these notes are notes in between these notes. I know I want to move up I might move my thumb up to the first 5 notes in the Fminor scale. I can solo on these notes. If I want to move my hand down from there I might drop them to the notes of a Cminor scale or any mode. It can even be the first 5 notes in the C phrygian mode.
Doing this I noticed keeps your fingers from getting tied up in the correct fingering of scales. You can even mix up with playing scales using the correct fingering. I guarantee if you try this type of thing in any key you will be able to solo in a few mintues.
I guess I now dub this my "Floating Thumb Technique For Keys."