The first thing that you need to realise is that the Nephilim get a pretty bad rap in the bible and popularist mythology. Generally speaking, most people on the planet either;
1) Don't believe they exist, or
2) Don't want them back
But, hope is not lost. Ever heard of the Annunaki? I hadn't either until I let my kids have freer reign with their viewing habits and they turned on a show called Ancient Aliens. Needless to say I've corrected that mistake but while the Annunaki really have little to do with aliens or nephilim in the manner in which they were originally worshiped, in modern times there has been an increase in a popularist belief among certain... well I was going to say spiritualist movements but even that in this instance is a misnomer; let's just say 'quarters'... in the idea that the Annunaki were really aliens that 'uplifted' us to mine gold for them.
This started with a book called The Twelfth Planet by author Zecharia Sitchin. Perhaps he has some followers? Convince them that it's the Annunaki who want to return to give us the blessings of some updated knowledge (your current situation is testament to that and you can even leverage some additional ideas from your patrons to prove the point), have the Sitchinites build the bodies for you, then your Nephilim can inhabit them instead of the Annunaki. Sure, there are going to be some divergent personalities and behaviours from expectation, but then the Sitchinites should have been careful what they asked for, shouldn't they?
Bottom line is that Kilisi is correct in stating that this is an impossibility and (let's face it) if it was possible, the Nephilim wouldn't need you to do it for them. So, either this is a test of your loyalty (the above has to be a pass mark at least) or they really don't know how to do it and think your fear could be sufficient motivator to find a way, in which case you are effectively outsourcing the risk to the Sitchinites.
So; I say try the bait and switch and see what happens. Either way, you've fulfilled your bargain.