1st add the EHDU license.
Under users and devices click add, under profile assign name and extension number, click the hot desking user box. Under the service details enter your COS with the EHDU options you wish to use, yes to external hotdesking enabled, enter your outbound prefix, enter the number associated with the external device. Under the Access tab, enter the PIN you wish to use.
You must have the access number programmed to be able to log the device in (system access points form).
If you want perm log in to work you will need to enable the Call recognition service on your trunks.
All of this is for MCD 5. 4-4.2 are similar.