Is there a simple way to run projects that use the vboxwrapper under Hyper-V instead of VirtualBox? Preferably by converting rather the existing image rather than building a Hyper-V image from scratch.

In theory I suppose it would be possible to use Hyper-V but simply converting the image is not enough.

vboxwrapper is responsible for creating the VM and starting and stopping it. I'm not sure but it may be passing some information between BOINC client and the VM while the task is running. It would be necessary to port vboxwrapper to Hyper-V.

Also, if any project uses a thoroughly stripped down image that supports only the virtual hardware Virtualbox provides and if Hyper-V doesn't use the same hardware you would need to edit the image and add drivers for the Hyper-V hardware.