I have had fun with Step Sequencer provided by Cie.
The only thin missing is to just click drag to sequence pattern.
Just wanted to suggest something like that to be possible in future releases of renoise since this could be usefull not only in this scenario.
THX for reading.
One thing what could be done, is simulate ctrl/shift click to perform area selections.
Simply make the tool listen for modifier keys and let it respond differently if they were pressed when a button was clicked.