Since I believe that Active Directory Deployment (publish or assign) of software packages is still restricted to .msi (Microsoft Installer) .mst (Microsoft Transform) and .msp (Microsoft Patch) files. It would depend on your ability to repackage the gadget file (usually default package .zip or .cab) into one of the supported file formats for active directory deployment.
As far as using Group Policy to defeat the users ability to manage the gadget I believe you only have four option, none of which it would seem would do what you want
Override the More Gadgets Link
Turn off desktop gadgets
Restrict unpacking and installation of gadgets that are not digitally signed.
Turn off user-installed desktop gadgets