the only iPhone wallet app offers NO WAY to include a transaction fee?
I can't elaborate much on your answer but can provide reasons as to why this market seems so bare.  Apple has shut down other providers of BitCoin wallets for "legal reasons" -- all due to the legal ambiguity of BTC transactions.  

Your best bet is to look into mobile-optimized websites that offer BTC transactions.  I'm unfortunately not too knowledgable on the topic - but at first glance, you might want to check out https://walletbit.com/, https://bips.me/ or something similar.  Happy hunting!