This is from the Tech Log thread - the ejectable, floating ELT called a Crash Position Indicator (CPI) has been around since WWIi. CPIs have fitted to helicopters, transport aircraft through the Tornado and Starfighter. The ELT is fitted into a floating "tumbling airfoil" and can contain a CVR/FDR.
Here's an example for the USAF C-141 original CPI, including multiple damage sensors throughout the aircraft and provision for a tape recorder for the CVR
AN/URT-26 Crash Position Indicator
Other offshore industry and military examples can be found on Google.
The extra cost over ELTs made the CPI unpalatable for regulators and airlines, but that may change...with modern electronics it can be a very much smaller device using the 406Mhz technology and solid-state memory for FDR/CVR:
http://www.hr-smith.com/images/stories/503-CPI.pdf