Yeah usually tab to transient, split, tab to transient, split, etc. while visually making sure it's tabbing to the right part and moving the cursor with the mouse to where it should be if I have to. Then Reaper has an action to create chromatic midi from item splits so I use that, open the MIDI, select all, open note properties and set them all to the same note.
Either that or Drumtracker, which fucking RULES but I have not been able to figure out how to get it to import the MIDI properly back into Reaper when dealing with tempo changes... So I either have to erase all my tempo data for the song and import the midi at one tempo which blows because I lose a lot of editing functionality or I do it the manual way.