Couple of steps come to mind for the truley gutsy...
1. Get 2 small buckets. Fill one with glue and the other remain empty.
2. Get Nurgle models ready near glue bucket.
3. Buy lots of beer and nasty food stuffs.
4. Binge drink for a few hours and fill yourself full of nasty food stuffs.
5. Hurl into empty bucket. :X
6. Dip models in glue bucket then vomit bucket.
7. Allow time to self dry, drips making great oozes.
8. Play with the most realistically nasty Nurgle army ever.
Would I personally suggest that? No. Would it make one hell of a Nurgle army? Yes.
But if you don't feel up to it, the guide posted is fairly good. Get some green stuff, perhaps some Nurgle banners and turn your normal Marines into disease filled rotting corpses oozing slimey goop. The beauty is that you don't have to be perfect with your Green stuff conversions, considering they are suppose to look nasty in the first place. ;Y