You can find here my succeed test with a water-soluble PVA Wire the SCAFFOLD and POLY PLUS PLA with a dual extruder mode on my ultimaker 2.
After many tests and help with the community, i found this parameters to print the SCAFFOLD with 0.3mm nozzle and the cura 2.7 in 0.2mm per layer. I 'm using a special head "Dual_Balance" but you can also use this paramters with you dual printer with 0.3mm of nozzle. You can find here the picture with all the cura 2.7 parameters.
For more detail you use this link:
The only problem that has occurred is a layer that is detached from the tower caused by my setting on CURA to clean the nozzles. so to avoid!