I don't think so. The reason is that on the older firmwares, metldr was the loader that contained all the others (except bootldr and lv0 of course) and lv0 was not really used for anything other than setting up the hardware. We already had metldr exploited.
Then in 3.56+ firmwares, Sony encapsulated everything into lv0. So lv0 is now the equivalent of what metldr was on 3.55 and earlier.
To my understanding, this won't help much with dongles which are no doubt signed with different keys.
For more information on how the consoles boot: