Very good suggestions; I wouldn't have a problem with any of them.
I also want to strongly applaud your first "if": [if] the evidence is irrefutable.
In the case of jesuashok and madtoperl, the evidence is irrefutable, as anyone who reads any of the pirated material will quickly see. But I'm glad you make the point, because it might not always be so obvious, and I would hate for anyone innocent to be unjustly accused of plagiarism, just because something they posted was coincidentally close to existing code or commentary, or because they had reposted their own work here at Perlmonks.
Ironically, this is exactly what jesuashok accused TwistedRaisin of doing, in this thread in the Perl Poetry section, saying "I found this same poem in twistedraisin". Clearly, of course, it's the same author in both cases, but such a fact might not always be so obvious, and even if we are quick to suspect plagiarism, we should be slow and methodical before accusing, lest we falsely condemn.
As far as code is concerned, it's very easy to coincidentally write similar or even identical code, especially if the code fragment is short, contains common/standard variable names, etc. We shouldn't assume a subroutine has been pilfered, for example, just because it bears the same name as the original.
So I would urge caution in looking for plagiarism. SamCG was appropriately careful in the way he handled his concerns about madtoperl's first poetry submission, asking simply "It's very remniscent of listen a lovely poem by Sharon Hopkins. Have you read it?"
Let's all be equally careful not to falsely accuse.