It was a while before I could drink soymilk. It just made me so gassy. Over time, and temprarily using some digestive enxyme supplements, my body got used to it and I was better able to digest it.
It really seems like you're body is only going to bother making enzymes for foods you normally eat.
If I were in your shoes, I'd try to find some "Red Field Peas." They are small and flavorful beans, easy to make, you don't have to soak them, and they can be used interchangeably with lentils in recipes (just allow for slightly longer cooking).
If you really want to add lentils into your diet, just add a little bit of them into normal bean-based dishes. Like, bean dips, burritos, chili, etc... Just add a small amount of lentils.
Edited to add:
There are different kinds of lentils, too. My Mom and I can't handle red lentils. Ugh... We both get so sick. We just can't digest them, and we don't really want to try!!!
I do well with green lentils, and my absolute favorite is French Lentils!
Give thanks to Mother Earth for Her greatest gift...
For without it, we would be lost.