Have you ever thought of doing a custom shroud for a GTX 680/70? I mean one that has an opening for the 620 tubing and also has a circular opening for the stock fan as well.
Something similar to the EVGA GTX 680 SC shroud (because it is pretty much flat) with an extra opening on the bottom / top for tubes. Or am I getting way ahead of myself here?

I'm just not a fan of modding the original shroud / don't even know if the 620 block could fit under it.