Can I place an electrolytic capacitor close to a solder point on a two sided pcb?
There may be more DFM issues than this and design issues such as heat dissipation from R to C.  

Use polyurethane bond all Cap to board AND insulate high voltage.

I recall 2.5mm air slot for 2kV transients creepage but here you use >1mm of polyurethane over solder joints and extra for bonding caps after initial tests.