Refilling is very easy. Just slowly drip ink on the felt in the outlet hole of the cartridge. When the cartridge appears to be full, remove the overflow with a tissue and... ready.
But there is no resetter available for these cartridges. So you have to switch off the ink counter of the refilled cartridge and refill monthly to avoid the head from running dry.
According to the Canon DK website the inks are the Chromalife 100 system. The inks for the PGI-5/CLI-8 cartridges are also the Chromalife 100 system, so maybe an ink set for a 5 cartridge printer of the PGI-5/CLI-8 generation will be suitable? But being the same system doesn't mean the colours need to be identical. You could ask Precisioncolors if they can supply a suitable ink set.
The pgi-5/cli-8 ink set is the right choice for the iP100 printer, as Peter said.
I think the colours are the same, because the OCP handbook recommends this ink for that printer.