Plastic platform for THT electrolytic capacitor?
Look for "spacer" or "capacitor spacer". They exist. 





Sources here and here. Can't say as I've noticed them being very common in the wild, however. 

They would probably need to be made from a decent plastic to withstand wave soldering and solvent cleaning. For careful and fast hand soldering you might be able to 3-D print a suitable shape- be sure to pick a material that meets electrical and fire safety requirements if you try that.