Please remember that all III-yod Qal prefix-conjugation verbs have the base /yiqtal/, even if they were originally /yaqtul/ or /yaqtil/. In other words, all three bases have collapsed onto /yiqtal/, just as all three suffix-conjugation verb bases have collapsed onto /qatila/.
Now, there is at least one III-yod verb that behaves like a segholate noun when jussive: יֵ֫רֶא (whose base is /yiqt/, just like the /qitl/-base noun סֵ֫פֶר). However, for some reason, its base becomes /yaqt/ when preceded by the waw-retentive, i.e. יַרְא.
As for יִהְיֶה, its jussive form has the same base as a III-yod /qitl/-base segholate noun, such as פְּרִי. Observe:
yihyayø was the jussive base (while yihyayu was the indicative base), of course.
yihyayø → yihya → yihy → (through homorganic shift from the yod to the i-vowel) yihī → (I have no idea why the accent shifted to the final syllable) yəhī
However, Drink is right that most of the time, III-yod Qal prefix-conjugation jussive verbs do not behave the same way as III-yod segholate nouns. יֵ֫רֶא and יְהִי are exceptions.