I am happy to say that my Dortmunder with Mandarina Bavaria came out very well. It was highly appreciated during a tasting session at the local club. When people start asking for more after the official end of the meeting, I think that's a good sign.
For myself, being a lager hater, I think I successfully managed to mask most of the lager taste, so I kind of liked it.
Thanks everybody for the good advice on lagers, Dortmunders, MB, water treatment, forced lager fermentation and carbonation methods, etc. etc.