Couple of options -
Hack a M
Show Image
(http://geekhack.org/attachment.php?attachmentid=4325&stc=1&d=1252424542)
Spend the big bucks
Show Image
(http://geekhack.org/attachment.php?attachmentid=4326&stc=1&d=1252425000)
I dunno. Sounds better than it works when I tried it. The top left row was great but the bottom left row was a PITA.
Ripster, were you able to split up the Return key?
Speaking of annoyingly sized keys, look at the bizarre freaks of nature I found today in Akihabara.
Show Image
(http://lh4.ggpht.com/_6WOoTO_7VuQ/S22TOSg54PI/AAAAAAAAAXw/uuTRMD9P8R4/s800/%2Fsdcard%2Fdcim%2Fcamera%2Ffeb6_9793.jpg)
Those arrow keys would actulally be quite good if the top of the left/right keys were recessed (like the capslock key). It would be the best of both worlds - easy to locate like a 'normal' keyboard, but big left/right keys you can mash away on.