It is not a real proposal, because it already works like that.
I know that a graphical editor would be preferred, but at the moment I could implement this quickly:

You can specify a custom phrase order with assigned lengths, variations, and rests! Please read the help that is displayed on the screenshot. I think this is quite powerful, but simple enough to remember.
Please let me know if you want to try this in the form of a beta version.
Thanks,
Attila

