I started my Key lime from seed about 5 years ago. It grew quickly and had a few blooms the third year but did not set fruit. the fourth year it bloomed a few more blooms but the fruit fell off. This year it bloomed and I had a bunch of fruit but many fell off when the tree went into stress when I couldn't water for about 3 days. I may have 24 limes remaining. I am not aware that ethylene gas will help it bloom. Keep it watered, feed it regularly with low nitrogen and phosphorus fertilizer. I also feed with Superthrive to give it a boost for blooming. My Key lime has grown as a tree. Some limbs tend to grow fast and long but I trim them back. Mine is about 7 ft tall in the pot and 4 ft wide. It sits in a cool green house in winter. I only heat when the temps are predicted to go to or below freezing. Citrus need lots of light. That is the biggest problem with citrus indoors in winter. Buy a dual or three light halogen garage stand light. Go to your local big box home improvements store or local auto parts store. THese lights stand on a tripod base and have 2 or 3 halogen fixtures on the pole. These will provide warmth and SUPPLEMENTAL light. Nothing can replace natural light. I've linked an example for picture purposes only.

Here is a link that might be useful: Light

Oops, I just looked at the link and that light is TOO expensive. You can get them on sale at the big box home improvement or local auto parts store for less than $50.

tsmith, why are you recommending a low nitrogen fertilizer? Citrus feeds at 5-1-3 ratio, so I think you would want a higher nitrogen content.

Nitrogen causes lots of stem and leaf growth. If in a pot, you are going to have to prune the growth or have a large greenhouse to hold them in winter. It is my experience that pruning the stems suppresses blooms. Phosphate promotes strong stems and stimulates blooms. I have to keep them small enough so I can handle them and move then in and out of the greenhouse.