According to Stephan Bodewig, the administrator of the Nokia Night of the Proms-fanpage on which we found the hidden source code information that Roxette is part of the 2009 proms, Per Gessle was seen with Dirk Hohmeyer, the promoter and organizer of the German Proms. They apparently met at the day of Per’s concert in Munich.
Here are the links for the tickets again:

Tickets for the German shows.
Tickets for the Belgian shows.
Tickets for the Dutch shows.

Bodewig still thinks that Per Gessle is doing the proms on his own as a solo artist and not with Marie as Roxette. But according to rumours that Marie will be in The Netherlands on wednesday (the day after the official NOTP press conference in Antwerpen) it’s most likely that it is indeed Roxette who will participate.