1) sell a reusable key for 5,000 cpoints that is specific to that lockbox. The key would have a 20 hour cooldown. What this does is it gives people a choice, pay 3 times the cost of a normal ship upfront and be assured to get it, or roll the dice with the master keys.
That's more than a years worth of stipends to open a box once a day. Cheaper than buying keys individually but it's still a bad idea.
I don't know about anybody else, but when I see any of those boxes I collect as many as I can and then discard them all. I only made the mistake of buying one key and then that was it. Now I tell my Chief Petty officer, who's manning the transporters, to beam them all out into the vacuum of space and then I have my tactical officer use them as target practice! It feels much better that way!