by process of elimination...and the
last one i tried, the 'A' button

looks great!
although the author might wanna have the action on the top screen since some ds screens are slightly 'hazier' on the bottom screen due to scratch free material.
edit: space ace would be awesome...and sound too!
double edit: just thought of this...what would be a cool mod is having to just touch the bottom screen for sword...or maybe just where you want dirk to go at the right time.