Hmm,
I was going to suggest Rosegarden, but you nixed that :(
However I'd like to re-introduce it but with a different slant.
How about actually playing your idea on a keyboard linked to
Rosegarden, then using the notation editor to clean up, create
repeats, etc.
This is exactly how I produce a lot of my work, but using the matrix
editor rather than notation.
--
Will J Godfrey
http://www.musically.me.uk