Adding a small ceramic .1 in parallel will do nothing for what happens inside non Low ESR capacitors, yes it may well lower the measured ESR of the 2 together but it's like adding a garden hose pipe along side the Mersey Tunnel to help traffic flow
Low ESR capacitors are not hard to find, the rule is to add 2200uf per 4 inches, a quick ebay search gives £6.50 for 5 rated at 35 volts, yes more expensive than £1 for 10 via Aliexpress for normal ones.
You don't need to add 2 X 2200uf for 8 inches, you can just use 1 X 4700uf.
It gets interesting if you go over 35volts as higher voltage caps get harder to find, the trick is to use 2X 4700 in series to get 2200 but at 70 volts