I use wetted out toilet paper. It feels all gooey but u simply press it into the well and let it dry over night. Then the edges can be filled with poster tac if you want.
When paint is dry simply pull out the now dried paper plug. Works well and does not affect the paint in the well....unless you used acrylic, I dont know how wet paper will soften it ?? I alwys paint with enamel.
Theuns