IPad – Apple Lightning to Micro USB

I know of no device that is sold to act as a write block that also allow full 1A charging, but Apple's patent covering potential upcoming changes to the dock connector might help you if you wanted a DIY hardware solution for the older 30 pin USB connectors.

In the mean time, you have several ways to secure the data without needing a custom piece of hardware.

1. Lock your iOS device with a passcode before connecting it. This ensures the data is encrypted.
2. You could go a step further and be ready to power off the device as soon as it's connected - shortening the window for the OS to be available to the charging station. The devices will still charge and shouldn't wake up unless it detects a disconnect/reconnect of the USB cord.
3. Be careful to not establish trust with unknown chargers and computers by tapping when prompted by iOS 7.

Furthermore, if you upgrade to iOS 7, anytime you connect to a computer which could potentially read your data, you are alerted to this fact rather than having the device share all data because it's not locked with a passcode.

This new "trust this computer" functionality prevents any access to your device's storage without a positive user step to allow that access.

The device won't talk data to the "charging station" until the passcode is entered on the touchscreen. (Or the astronomically unlikely but theoretically possible chance that the charging station provides the one and only unique to you secure certificate generated and stored on your primary iTunes computer.)

The charging station can't try entering passwords one by one - so it's not like you are at more risk by charging an hour versus 2 minutes.

I'm trying the very same thing. I made one myself but the dock station didn't see anything connected so didn't enable the audio signals. I then saw a cable 30pin to 3.5 on the Internet which I ordered and this is doing exactly the same thing. The dock station only uses pin 1 or 2 for signal Gnd and pins 3 and 4 for left and right audio signal.