its a little more work but you could get a plastic bag and press it into the cupholder holes
spray some expanding foam into the bag once dry you would have the perfect shaped plug
over the top you could then cover it in vinyl / leather.
the long panel the cupholders are fitted in unclips easily hold the panel at the back and give it
a good pull upwards until the whole panel is free, remove wiring plug for the controller then
turn panel upside down and you will see 4 screws that hold the cup holders in place, remove
holder and then apply the cover over the top and refit.