Now, about that home-made dome. . . . where are the pics and the DIY report?
I'm sure that there would be some very interested observers around here. . . . me for one!
Bruce...
Would also love to hear your DIY tale! Off to Anilao and Tubbataha in 2 weeks and would love to find some sort of wide angle option!
Steve
Here are a couple of shots on my DIY dome... 


Items used and how it's done:
Items
1 unit of Inon Dome Port for UWL-100
1 Couplings Connector (PCX 56 - 43 - 4" x 3") PipeConx
How it's done
Insert the Inon dome port into the coupling connector (larger end - 4"), you may find it difficult to do so. Use a hair dryer to soften the connector and then apply a lil bit of silicon grease for easy inserting of the dome.
Adjust the dome & coupling to level, then tighten the stainless steel banding to secure the dome.
Once the dome is securely tighten, proceed to cut the bottom part of the coupling. Cut according to the bottom part of the stainless steel banding (reason - for better and closer fit to the housing lens port). DO NOT over cutting the edge, cos the banding might not be able to securely tighten the coupling to the housing.
Now, apply a lil grease on inner part of the coupling and insert it over the OEM housing lens port (not to close to the housing - 0.5 in apart). Tighten the stainless steel banding sparingly (hand strength tighten is enough). "Ting!" Now, you have a DIY dome port for your Canon OEM G10 housing. However, there are a few precautions that you need to take for the dome to work effectively.
Precautions
1. Attach the dome in a cool and dry place, to avoid fogging.
2. Note that the coupling is semi hard and when under pressure, it tend to contract closer to the housing port. Make sure you adjust it according to proportionally during your descend. If not, the coupling tends to bend to one side. This problem is solved when you reached 8m and below.
Pros & Cons
Pros
1. You can now use the actual built in 28mm of the G10, instead of the 28mm with magnification, underwater.
2. It is an external attachment, so no worries on flooding. You can still use it even when it floods, however it will no longer be the actual 28mm.
Cons
1. Need to pay attention during descends and adjust the coupling
2. Slight vignetting at the depth of 7m and above
Well... Just like a saying, you win some, you lose some. Have fun experimenting with it and I hope the info helps. 
Ed.
PS. It is your own responsibility if you should decide to try it so please practice with caution. I am NOT gonna take any responsibility for any damages or flooding under any situations, during the course of your DIY. 