Try just taking it off. I took mine off of my Selmer and I haven't missed it. You pretty much always play with a peg or a neck strap on the bass, so the thumb rest really isn't doing much.
If you do end up wanting it back, you can always worry about the longer thumb rest at that point.
I just tried this a few days ago on my (low Eb) Selmer bass. It's so much better!I removed the thumbrest and it seems to work just fine... thanks!
I was having trouble navigating the inner RH pinky keys (i.e., RH low F# and low E), and found it difficult to reliably keep enough pressure on the RH ring finger key (low G) while playing any of the RH pinky keys in quick passages.
When I finally removed the thumbrest and tested to see where I might reposition it, I was amazed at how much better my right hand felt without the thumb rest. For me, it works equally well when standing (with the bass supported by a strap) or seated (where I use the strap in combination with a peg).