I read the OP's question as "[I am flying on an internationalitineraryy], can I invite a fellow traveller on a domestic itinerary to one of the Priority Pass lounges".

The OP can, in theory, go to the domestic airside area (there is no one to stop him from doing that), enter the lounge and then go to the international area when he is done.

What I can't guarantee is whether the lounge staff will allow the OP into the domestic lounge with an international BP. I guess it should not be an issue if he explains that he wants to spend some time with a friend who is flying on a domestic.... and if one of them refuses, there are 3 other lounges that the OP can try (DME Airport authority lounge, S7 Business Class lounge, S7 Comfort (pay in) lounge and the UTG lounge).