As Paul has mentioned, you could do something with the security slot, but that might just mean that the empeg gets trashed as someone tries to lever it out with a crowbar.
There are another couple of options;
Someone has recently made a display extender that could be used as a basis for a removeable display idea where the main unit is more securely fixed. However, there are significant technological details that would need to be worked out to make this work. Firstly the display would need to be physically modified/encapsulated into a docking case (and a corresponding dock designed), and secondly you'd need to do something electrically to ensure that there is no power to the empeg during docking and undocking.
Neither of these are insurmountable to someone with the skills, dedication, time and resources but it's not going to be a walk in the park. No one has felt inclined to do it yet.
The other option is to do a custom dash that completely encloses the empeg so that it cannot be removed without the dash being assembled. Someone has done this, there are pictures on riocar.org somewhere.
Both of these ideas have some drawbacks though. Firstly, it makes it difficult to add music to the empeg. It is possible to work around this with some thought, but again it is hassle.
More importantly though is that neither of these schemes prevent the empeg being stolen. Ask Loren about car theft sometime.
_________________________
Mk2a 60GB Blue. Serial 030102962
sig.mp3: File Format not Valid.