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Quenya is known to use "i" (or before vowels "in") as the conjunction "that", as in "I know that you did it" (istan i carnelyes). In English, such a "that" construction can also mean "so that", implying intentional causation (like Jesus saying "I have come that you will have life"). This use of a "that"-sentence isn't really attested in Quenya, I believe, but it is not entirely implausible, either. Do people have any thoughts on this?
I think you may have posted this in the wrong place.
To your question - we have an attested example of pretty much exactly this in the Koivienéni Sentence. Though I can't find other examples, and this does come from earlier drafts of the language, so take it with a grain of salt.
That being said, I would prefer to follow the attested example above and simply use i, rather than resort to the neologism that was made specifically for that, since it seems to me that such a neologism is superfluous.
Also a point for the record - that i that is used to open a subordinate clause is just i, and never in, e.g. Átaremma i ëa han Eä etc.