Who will discuss semantics primes if not us? Any forum you are aware of? I'm afraid they are discussed nowhere.
Guaspi? Any other conlang group? University level linguistics courses? Gismu aren't primes, the set of UI aren't meant to be primes, and nothing in the language is meant to be the most basic set of anything. We *really* need to hammer that into everybody and start adopting a policy of using what's there instead of reinventing the wheel. Look, and I mean seriously and earnestly look, for a solution using what is already available to you. If it isn't a problem, don't fix it, and if you absolutely are completely unable to do it with the current grammar, we'll talk then.
What is more, in this case I have a clear feeling that {.a'o} *is* a prime. But probably it's only my philosophy.