I'm not an expert on this subject, but I grow a number of lilies and know of no way to make them "delay" their blooming.

Like you, I love those Orienpets. To get extended bloom, plant other kinds of lilies in the same general area. My Regale lilies (trumpet) bloom slightly before the Orienpets (although there is a lot of overlap), and my Oriental lilies bloom mostly after the Orienpets. Among the four different types of Orientals I grow, Casa Blanca blooms later than all the others.

If you added Asiatic lilies in there, they are usually the earliest blooming lilies--should be done before the Orientpets even start.

Done that way, you can have nearly a couple summer months of lily blooms.

Kate