I have some broken panels on a Honda Scooter.  I have a hot melt wire repair tool that can repair and strengthen cracks by melting in wire clips from the reverse side of the panel but I have some pieces of plastic missing in some small areas. I was wondering if I could blank off from the back of the panel and use the actual hole as a mold and pour resin straight into the repair or do I need to make a pattern from clay and then a silicone mould and pour into that?  I thought I would shape the damage with a file and give the edges an angle and perhaps hot melt the repair in with my wire clip tool.
Any thoughts?

You could patch from behind with carbon fibre or grp, however it very much depends on the plastic.  Some plastics are inert and very hard to bond to, others will bond fine. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant