You may like the idea of using some 5 note scales, such as Chinese and Egyptian stylings, with use of octaves (C D E G A) and (C D F G A#) respectively. I'd personally love to hear this done, but thats just me.. Another 5 note scale with you might use could be Pentatonic Majeur (C D E G A). Another thing you may be interested in doing (which also is personally appealing to me haha) is to try out some arpeggio style scales (Major 9th). I was thinking, you may want to shorten the low C, in this case I've assumed it's been shorted so it's now a C#, in this form you can use the Enigmatic scale (C# D F G A B C) if you shorten the E and make it an F. Some other stuff possible, Iwato scale (C# D F# G and the Hirajoshi scale (C# D# E G# A). Anyhow, once you change the pitch of the low C, obviously there's alot more options, sorry I didn't keep to the octave interval rule aswell..