"dpkg -i package_name" from the command line, or if "appinstaller" ever makes it out of extras-devel, you can just touch the deb file once downloaded to install.

How easy this would be to implement into the ovi store, I don't know, but I imagine the download link could redirect to a page asking for an IMEI to validate purchase (kind of like nokia does), then prompt to download the deb archive individually.

Not the most elegant solution, but better than say, having a separate repository for each application.