The usual way of supplementing is to dust the insects at most feedings with a phos. free calcium powder to help make up for the usually poor ratio of calcium to phos. found in most feeder insects.
Most people dust twice a month with a phos. free calcium/D3 powder to ensure that it gets some D3 and leaving it to produce the rest from its exposure to the UVB.
The vitamin powder is also used twice a month. Most people use one with a beta carotene (prOformed) source of vitamin A since it can't build up in the system....an leaving the owner to give the chameleon some prEformed vitamin A if necessary.
Your gutloading/feeding of the insects is also important.