Can I use the nVidia controllers selectively for an application?

I recently installed Ubuntu 18.10 on my laptop with nVidia MX150. Then I added the nVidia drivers from the Additional Drivers section.
I use an application called DarkTable for photo processing. This application works much better with OpenCL when using nVidia drivers from Prime Profiles.
For anything else, embedded Intel Graphics is more than enough. I have read previously that nVidia Prime Switch is allowed only for the entire desktop session. Is it still the same or can I use Intel for everything else and nVidia only for DarkTable? nVidia consumes too much battery. (I think nouveau still does not support opencl)