But If you don't mind changing the wallet, you can try GreenAddress. I think it's the only (excluding Bither because it's unstable) open source wallet that supports both iOS and Desktop.
GreenAddress was actually renamed to
Green: Bitcoin Wallet for mobile devices. I have tried the mobile version and it worked fine on Android. @zxbit, if you create a new wallet in Green Wallet then you will be able to use your new recovery phrase (the seed) in most wallets, including Electrum. This way you can recreate your Green Wallet addresses in Electrum on the desktop
Edit: Use a different wallet than GreenAddress.
I don't think so. These versions are multisig-wallets 2/2 too. You only have one BIP39 seed, and you need two to recover.
Actually, you're right. I was quite sure that I could use Green Wallet while being offline, but I have just double checked that and I am wrong. Normally, I would have recommended
Samourai Wallet, but it hasn't been released for iOS, yet.