I think you could create a new table view, based on the same one you have now. But, change te relation in "not equal" instead of "equal". Then your portal shows the items that are not equal. The only thing is, if you use this solution, you have to built another form to show a portal with the records "not equal".
If you want to use the same form, you could base the relation on a global field, instead of a table, and change the value of the global field to show the other view. (Equal or not equal).
Where I used "table view", I ment "Table occurrence". (Sometimes confusing if your native language is not English).
Thinking this over, you can make a copy of your website table (second table occurrence) and connect this other table occurrence also to your Connector table, with the option "not equal". In that case you can create 2 portals on one form, one with the websites with access and one portal with websites without access. You could place the second portal in another Tab if you like.
one way to get such a list is to use Go to Related Records to pull up a found set of all permitted web sites, then use Show Omitted Only to show all the ones that are not permitted. This can be popped up in a small modal window.
Here's another option:
Define the following unstored calculation field in Employees with a text result specified:
List ( Conector::SITErecid ) & ¶ & -1 ) // the -1 assures that this field always has at least one value that does not match to any record in Sites.
If you name it cSiteIDList, you can relate it to a new occurrence of the Sites table like this:
Employees::cSiteIDList ≠ Sites|Excluded::STrecid
Sites|Excluded would be a new Tutorial: What are Table Occurrences? of Sites and a portal to Sites|Excluded would list all sites that a given employee is not permitted to access. The same relationship could also be used as a drop down list of sites for selecting sites in a portal to your existing Conector table occurrence. This is, in fact, a modification of the typical dwindling value list as demonstrated in: