Wait, the d2v (DGIndex indexing files) does not need DirectShowSource filters (LAV or ffdshow), they are frameserved with DGDecode.dll plugin. Therefore I cannot understand what you are trying to do.
About DGDecNV usage, you can easily tweak the AviSynth script directly in AVStoDVD. Go to 'Edit Title'/'AviSynth' and toggle off 'Auto AviSynth Script'. Then you can edit the script to use whatever plugin/function you want.
Bye