[Koha] Some doubts about issuing rules

In our library we have a situation that we don't fid how to represent it with the current schema of issuing rules, maybe you can give us an idea. For every biblio we purchase we give a special treatment for the first item of that kind we purchase. That items are labeled different and their a called "room only items" (ejemplares de sala, in spanish). This books are only borrowed in house during week days; but on weekends they're borrowed till the next weekday (tipically monday). The remaining items of that biblio fit on the standard issuing rules. We want to enforce this rule but we don't find a clear way of doing this, without modifing some CGI and maybe the database estructure. Any comments will be appreciatted Andres