My initial thought was that with a small modification to sixpair, it would be possible to feed it an arbitrary BD address, so I started poking around in the source – and found that the feature is already there :D
You need the BD address of the device that you want to pair with the sixaxis – get this with hciconfig – run it (on the N900 – or whatever system) and you’ll hopefully see something like this (I don’t have an N900) :
# hciconfig hci0: Type: USB BD Address: 00:1A:80:2C:BE:D0 ACL MTU: 384:8 SCO MTU: 64:8 DOWN RX bytes:87170 acl:1503 sco:0 events:62 errors:0 TX bytes:574 acl:22 sco:0 commands:21 errors:0
Plug your sixaxis into some other machine via USB, grab (and compile) sixpair.c and run it with the BD address
wget http://www.pabr.org/sixlinux/sixpair.c gcc sixpair.c -lusb -o sixpair ./sixpair 00:1A:80:2C:BF:D3 # use your own BD addr here
And that should be about it – unplug the sixaxis, continue with the instructions from the previous post and when you press the PS button, everything should work as if by magic.
If it does not, get more magic. Either way, leave a comment and let me know how it goes :)