So, it's coming up for 2 years later, so probably time for an update on this!

In short - it works!  The Micro:Bit is programmed, and mounted in a socket on a RC2014 prototype board, and it squirts code in to the RC2014 as if it was being typed in.

The 5 x 5 LED grid shows which of the 25 bits of text are sent to the RC2014.  The two buttons allow you to go left or right through the LEDs to select which one you want, then push both buttons together and it streams the ASCII string out of the serial port.  It isn't the most sophisticated of code... but it works :-)

The circuit is very straightforward, simply connecting to the power, Tx and Rx of the RC2014.  The 5v from the RC2014 goes through a 3v3 regulator to power the Micro:Bit, and the Tx from the Micro:Bit goes via a jumper to the Rx of the RC2014

This board gets used a lot, particularly at Maker Faire or other public events, where I want to program the RC2014 to do something interesting but I don't want to spend 20 minutes typing in stuff.  The great thing is that it just works.  Plug it in, select the appropriate template, push the buttons and it's done.  However, the usefulness to other people is likely to be limited, so I won't be developing this any further.