Final update: It's worth noting that you can still get colonial nations on different continents, if your capital isn't in a colonial region. So if, for example, your capital is in Bermuda, then then you can still get CNs in south america. The good news is that I'm pretty sure colonial nations won't form in provinces with a land-connection to your capital.
With this in mind, your options for no CN's ever are:
Start or become an OPM, then move your capital to a colonial region, or:
Colonize ONE of: Bermuda, St Helena, the Falkands, or possibly the Galapagos islands ( I don't thiiiink they're in a colonial region), then colonise a province in a colonial region, on the continent you don't own a province in (that is, south america if you took Bermuda, North America if one of the others. Or Australia.), and move your capital there. Now your capital is in a colonial region, so you'll never get get colonial nations. Wasn't that fun?
Incidentally, if you do this as the HREmperor, you pretty much make the empire hereditary, since new emperors have to be on the same continent as the previous emperor.
If you do it as Ming... Nothing special happens. But thinking about it made me giggle for some reason.