How thick is the tubing or how much thicker is it? If the latter then you're going to need to give us another cooler/tubing to act as a comparison. If you're asking about the H100i's tube diameter, it should be around 10/12mm
considering how the original H100 had 6mm ID 8mm OD tubing.
I would like to stress though that modifying the tubing will void your warranty and in essence what you're doing could've been done on a custom level watercooling kit for less and with greater experience gained in the process.
Could you parse more details of your case project?
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in case you'd like to live dangerously,
here's a link for you to check out. On another note, you may want to check out the watercooling sticky(in my sig space) since I mentioned that modding the unit will eventually lead you to perform bi-yearly maintenance of both coolant and tubing changes.