Customize Android 4.0 (ICS) Bluetooth HID
Custom keyboard layouts is an official feature of Android 4.1 Jelly Bean. 

It's called "User-installable keymaps", see more here.

If you don't want to wait/upgrade:
Besides this, Android uses  keymaps also for bluetooth HID devices (your device, some number keypads, Apple bluetooth keyboard, etc.). More info how to change this is here.