modifying the CS sequencer for launchpad: note length values

i'm trying to find a way to get better control over note length when inputting notes into the CS sequencer from the launchpad. my idea was to be able to hold down a note (for the start position) and then pressing another note of the same pitch (for the end position). for example, if i wanted to input a note with a duration of 8 steps, i would hold down the 1st step button and then press the 8th step button. i think there should be a way to implement this because in the ableton midi editor, there is a "preview" button that if activated, you can hold down a midi note from any external controller and then use the left/right arrow keys on your computer keyboard to set the note length. if that combination can work, then there should be a way to program it for the launchpad with max for live. any ideas on how i could do this?