Is there a way I can make my own oil to refill a Glade Plug-in container?
I wouldn't. These have been linked to several house fires as it is. If you made a refill and it had a different melting point, it could be very hazardous.
There has been a lot of discussion over the years about how to refill Glade Plug-ins rather than throwing them in the trash. This page collects advice about refilling glade plug-ins.