After a bit of surgery in June 2012, I found it impractical to play the keyboard instruments (marimba, xylophone, vibraphone, glockenspiel) by gripping the mallet between thumb and index finger. This photo should clarify the issue:
A few months following the procedure, I began experimenting with alternate grips that did not require use of the thumb. Here is one example of something I tried, which is derived from the Stevens four-mallet grip:
Although a necessary part of four-mallet technique, I found this grip awkward when holding one mallet. After a few more failed attempts, I discovered the following grip:
This modified grip has worked for me, and I now use it with both hands to provide a more balanced sound. I should note that this grip has not worked on snare drum because a drumstick is much thicker than a keyboard mallet and does not ride comfortably between the index and second finger. I have therefore continued to use the traditional grip on snare. As a result, my long rolls—which were never anything to brag about—are rougher than before the surgery, and my right hand still lacks stamina more than a year later.
Fortunately, I can still hold a tambourine comfortably in my right hand. And since my thumb rolls always sucked, nothing has changed.
I’ll get back to you if I come up with something completely different for snare drum.