Using a variable as the project url in Supabase plugin

I have searched and not found this. We are building in the Supabase hosted version but when we launch it will be self-hosted. In preparation, thought it would be a good idea to use a variable for the Subabase Project URL when conffguring the plugin. Is this possible. If so how do I see the variable when configuring the plugin? I am a complete newbee to WeWeb and I learn by playing around.