I'm no JUNOS expert, but you might want to include some more details into what you're trying to do exactly. Are you trying to view the config on your Juniper device in set commands or are you trying to convert an xml config that was stored externally and convert that into set commands?
If you are trying to do the first, I hope you've already found your answer and found that you can do "show | display set" on your Juniper device. You can also drill down into your stanzas like "show interfaces | display set".
I would imagine you could use SLAX or XSLT for the latter situation.