If you haven't yet, you may want to try asking on the Vine Forum...or maybe the Tropical Forum.

Additionally I found the info below on line.

One of the most impressive climbing plants which also grows well in subtropical climates. Woody vine with large fragrant white flowers resembling lilies, and lush tropical foliage. A strong growing climber which can reach 10' to 20' (3m to 6m) in full sun. Large, highly fragrant flowers appear in trusses particularly during the cool season in tropical climates. The leaves are glossy and dark green on the upper leaf surface, on the lower leaf surface they are hairy. Young shoots are also covered with brown hairs.
The Easter Lily Vine is considered to be a tropical plant, while some people say it is hardy to light frost. However, cold winter or lack of heat/light could be the reason why it doesn't want to bloom. Try to apply bloom-booster fertilizer during hot season (according to instructions, and do not over-fertilize!). Even here in subtropical Florida it is not easy to make it bloom. While in Thailand these plants are almost in every garden and bloom like crazy.

Sue

Here is a link that might be useful: Vine Forum