From what has been posted here, it seems that most people start the liver cleanse before the parasite cleanse.
Have you tried safflower oil? It's much lighter, easier to drink and seems to cause little or no nausea. You might only need 1/2 cup of grapefruit juice, since the GFJ can overpower the safflower oil otherwise. Actually, too much GFJ can cause nausea.
Let us know how you do. If this doesn't work, I have some other ideas, perhaps others will as well.