I suggest just using Riivolution to play the game. The Summer Sun Special has much too much ASM coding which currently requires Riivolution to implement, therefore the game will have lots of major glitches and is not worth trying to build into an ISO. The Winter Holiday Special can possibly be made into an ISO but will suffer some minor glitches in doing so and at least 1 level will not work at all. I saw this also from the Dark Umbra forums:
Newer SMBW is going to be maybe the best wii game ever and we won't be able to play it on Dolphin. I consider this a pretty major thing and really hope they can do something with it. Unfortunately, loading of all the new assets will just not work unless the devs reopen this issue and work on it:
