I don't really have a linguistic background and I'm not even sure if this qualifies as true declension but there's certain compound words that act as conjunctions semantically in Arabic that seem to fulfil what you're looking for.
Let's take the word ma3-'anna (3 representing a voiced pharyngeal fricative ʕ ). It's two separate words ma3 (with) and 'anna (that) acting semantically as a conjunction with the meaning "even though" and it just so happens that 'anna is a word that acts a bit like a verb by taking on a myriad of "pronoun endings" that indicate person, number, and gender:
ma3-annahu (even though-he)
ma3-annahumaa (...they, dual)
ma3-annahunna (...they, feminine)
ma3-annaka (...you, singular masculine)
ma3-annaki (...you, singular feminine)
ma3-annakumaa (...you, dual)
ma3-annakum (...you, plural masculine)
ma3-annakunna (...you, plural feminine)
an example of its use can go something along the lines of:
لم يذهب إلى المدرسة مع أنه لم يكن مريضا
lam yathhab ila 'l-madrasati ma3-annahu lam yakun mareeDan
not go-he to the-school even though-he not be-he sick
He didn't go to school even though he wasn't sick.