You mean that there is someone else with the 888 and ST2 pairing?
You can fit the bicycle sort of digital speedo quite easily. Glyn has done it on his ST2 road bike, it was quite straightforward once he'd worked out the pick-up position.
I'm not sure that I would want to do the digital thing on an 888 though, it wouldn't be quite right somehow. To be honest, I haven't had the 888 long enough yet to have had cause to examine the speedo drive so I don't know how it differs from the 748/916/ST2 drives which I believe are all the same - is it a different cable fitting? If it is, there maybe somewhere that can make you up a speedo cable with a 916 fitting at the drive end and a 888 fitting at the speedo end.
If the speedo drive is geared differently you might be able to get a converter made up - a bit like those km/mph converters that fit onto your cable.
Just a couple of ideas - even if they're crap ones.
BTW Frank: you can get 65mm adaptor plates but they are sooooooo ugly