I'd love for someone more knowledgeable to tell me I'm wrong, but I suspect it might not be possible (at least via File Packages for NIPM/NIPkgs).
The list of possible installation roots is here: https://www.ni.com/documentation/en/ni-package-manager/latest/manual/installation-target-roots/
The highest-level option (from a directory point of view) is "BootVolume", which allows you to build any arbitrary path relative to "C:\" (assuming you're booting from C:\, e.g. "BootVolume\MyArbitrary\DirPath\blah.exe" will install to C:\MyArbitrary\DirPath\blah.exe) but doesn't help you get to "D:\"
The other options can be useful to create fewer intermediate directories (e.g. choosing "ni-paths-LV2020DIR" and then a subdirectory for "vi.lib" is fewer than "BootVolume" and then nested [Program Files (x86), National Instruments, LabVIEW 2020, vi.lib] directories), but they don't give any additional flexibility that I can see - the toggling could be useful in some circumstances, but the directories could always be specified relative to BootVolume.
The leaves you, I think, with the WinInst Packages.
If you could build an MSI file then I suspect the range of options is wider - you could give it a default path to D:\ probably and if you wanted allow the user to edit that (or not...)
Maybe InnoSetup or similar (I've never used this, but a few people have said good things about it).