If a cash (non-bid) upgrade is available through Copa's website, it usually means Z space exists, so a confirmed PlusPoints upgrade is then available through the online tool posted by cfischer.

Only downside is the terrible redemption value - it's 40 PP per leg... so for example, an MVD-PTY-IAD itinerary would require 80 PP to move into business, and it wouldn't even be lie-flats.

Once you have the upgrade you will almost certainly have to call Copa the have them realign the ticket. The Miami call center can usually do this pretty quickly.