The use of royal jelly makes huge differences in grafting takes numbers, especially in times when a major flow may be lacking.
I find the following in order of worst to best...
Purchased royal jelly (I never buy as it's probably foreign and tainted)
Wet grafting (diluted honey)
Using your own produced FRESH royal jelly from any of your hives
Using royal jelly from the hive you graft into.
In periods of late summer, I can improve my grafting numbers dramatically by switching from diluted honey (Which works when conditions are optimal) and going to royal jelly.
To make the royal jelly stretch, use some diluted honey as a base to wet the cup down, then "feather" in some royal jelly with a fine paint brush. You really only need to "scent" the cup, and the bees will think it's been worked on by other bees and they will take it fine.