Show different albums to visitors from different sub-domains

[karj]

I want to operate the one set of coppermine files to which several sub-domains refer.

When a visitor clicks a link to the common coppermine gallery I would like the link to carry an id which coppermine intercepts and subsequently shows only the albums in one category - at least at first.

If no id comes with the url then all categories should be shown.

I have had a quick look at the php and can see it would take me hours to find a way to do this, and I am sure someone familiar with it would come up with a clever solution quickly!!