title_body: Lemmata in a prefixing language
upvoted_answer: You could just list them under the stem in that case. If you can easily reconstruct the infinitive by a simple rule, then that would be the easiest way. There is no law that states that you always have to put the infinitive as the main dictionary entry. It's only common practice in most Western languages because it suits the way they work.
  Another possibility would be to look at how other languages deal with this issue. For example, Indonesian verbs also tend to have prefixes; I'm not sure what they do in the dictionary. In Arabic, I believe the root is in the dictionary, ie the three core consonants from which the other forms are derived.
  Just do whatever works for you: it's your language after all!