The manual (German) makes no mention of remote management, maybe worth trying to update firmware of unit , but I cannot see any options inbuilt,
Next time you are at your parents, disable Remote Management and see if you can still gain access to it from the LAN ?
Apart from that and the Virtual Server option I detailed above, I have no idea 
In a completely sane world, madness is the only freedom (J.G.Ballard).
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