Thanks for the replies.
disper indeed does not have (proper) support for more than 2 monitors. But with a bit of hacking I managed to achieve what I need:
disper -d DFP-0 -s
echo -e "backend: nvidia\nassociated displays: DFP-0, DFP-1\nmetamode: DFP-0: 1920x1200 @1920x1200 +1600+0, DFP-1: 1600x1200 @1600x1200 +0+0\nscaling: stretched, stretched" | disper -i
disper -d DFP-2 -s
Apart from using the -i option I was unable to enable both my 2 monitors again. However, if I omit the disper -d DFP-0 -s, both monitors are enabled but only a box of 1280x720 can actually be used?
Anyway, these scripts are probably far from elegant, but for my situation they get the job done!