Yes, if you have both
wubi.exe and the ISO image for the same release, you can make Wubi use the ISO so it doesn't have to download the files again. This makes installation considerably faster!
It's advisable to check the MD5SUM on the ISO image, to make sure it's good.
Put the ISO image and
wubi.exe in an empty folder.
Technically there could be other files in here, but it would be confusing, and once you get additional Ubuntu ISO's in there, which sometimes happens for users who are trying different versions, it would be a bad situation.
wubi.exe to install Wubi.
That's it. With the ISO image in the same folder as
wubi.exe, the Wubi installer will automatically attempt to use the ISO image (and assuming it's an ISO for the same version of Ubuntu, and the ISO is not damaged, there should be no problems).
Assuming everything goes well, it should be possible to install without even being connected to the Internet when
wubi.exe is run. However, if possible, it's recommended to be connected to the Internet while installing Ubuntu (whether you install it inside Windows with Wubi as you plan to do, or alongside/replacing your existing Windows or other OS by by booting a CD/DVD?USB).
Remember, the Windows installer (
wubi.exe) and the ISO image should be for the same release of Ubuntu.