Yeah someone used to sell a flashlight head you could stick on ELT-10 batteries. I guess it wouldn't be too hard to make other than it's sort of pointless. I replaced my ELT-10 with one that takes D cells a long time ago.
You are not, though you are well advised to do so.
You can install a TSO C91A unit (these are the ones that have the remote activation/monitor). The FAA wishes you wouldn't however. In a heavy handed attempt to drive the market towards 406, They won't approve any new TSO C91A units but those with authority to produce them as of 2012 can continue to make and sell them and you can install any of those.