Jake Allen posted a nice picture of his Bluetooth CD-i setup on Console Purist. It is based on the SNES2CD-i Adapter trick of which you can find tutorials here. The trick here is that the arduino case is actually built in the CD-i player itself, so you can connect the wireless part directly to your CD-i player. In this way your CD-i player is truely wireless. Moreover, these 8bitdo SNES controllers are by far the best controller I've ever experienced on CD-i, they even surpass the Gamester CD-i gamepad. If there is one mod that is beneficial for you and your CD-i experience, I'd start with this wireless SNES2CDi mod.
SNEStoCDi is an Arduino-based project that allows to use a Nintendo SNES (Super NES) / SFC (Super Famicom) gamepad on a Philips CDi player / game console. SNEStoCDi requires no more electronic than the Arduino itself. It's a pretty easy project for anyone with basic knowledge about Arduino and soldering.
[Thanks, Jake Allen]