Private prosecutions 101:
There is no way to prevent someone laying criminal informations. Each has to be considered on its merits. The technical name for declaring a litigant vexatious is a "civil restraint order", the clue is in the name: it can't be used for criminal prosecutions. It's not possible to refuse an application prospectively because the judge or legal adviser won't have considered the merits of an application if they haven't seen it.
The system is fairly efficient, the applicant completes a written application and a judge or justices' legal adviser considers it without a hearing. The longest I've ever spent on an application was half a day (it's articulating the reason for refusing that takes time) and they usually take much less than that. It's rare for hopeless applications to get through.
That means we don't (at the moment anyway) need the same provision as the civil courts - the procedure means weak hearings are strangled at birth. If EWE had gone down the criminal rather than the civil route the cases he supports would never have got to court at all.
A lot of things waste court time, but Waugh isn't a particular problem. He's only applied 2 or 3 times, they're quickly dealt with in the office, and it's not likely that any judicial review would get past the permission stage. That doesn't mean that what he's doing isn't irresponsible and futile, but part of the futility is that he's using a process calculated to weed out this sort of stuff befeore it gets to court. Prosecuting ministers makes his task harder and the courts' easier, as only one court in the country can consider the cases, so in fact it's always the same judge.