I built a structure out of PVC pipes and wrapped it in foil, and was planning on building my RKT design around the pipes. Unfortunately no matter how much I tried, they stick more to my hands than they did on the structure.

I have read that I can use corn syrup or melted marshmallows on the pipes before trying to add the RKT. Which one works best, or do I have any other options. 

Any advice would be much appreciated!

Here's a Cake Central Tutorial that might help you. 

https://www.cakecentral.com/tutorial/57020/pvc-structure-for-cakes

Yes, RKT's can be a bitch to work with.  I use melted chocolate on my structure, squeeze the RKT's onto the structure as tightly as I can, then wrap as tightly as I can get it with cling wrap and let it set until it firms up.  If the piece is small enough, I put it in the refrigerator.  Once it has stabilized and the RKT's set, remove the cling wrap and proceed to carve or decorate.