The support team argues that this won't be supported because it is bad for SEO without any other considerations.
The support team is known to be rude and to divert issue, pointing at other issue rather addressing the problems, like the example above:
Multiple domain support vs SEO ethics.
It took them 4 post and 2 forum "hero member" to finally admit that "It is not supported and will not be supported."
I wouldn't advise to expect much from the support team even if you don't need multiple domain support pointing to your site IMHO.
I've seen many threads on their support forum that speaks for themselves... just do a search for the word "rude" on the forum and you will understand what I mean.
I'm sorry if you feel we've been rude to you, that was certainly not our intention.
However, it does seen we failed to convince you, so I will say it again here for the record, and for other users:
Don't do this. This is one of the biggest mistake you can do from a seo standpoint, and I can only confirm that sh404sef will continue to not allow this.
Being able to access your site through several domains is just a significant loss of ranking. I am sure everybody now knows and understands that you must not access your site using both www.site.com and site.com, but for some reason many people don't accept that accessing it through site1.com, site2.com and site3.com is exactly the same problem, only bigger.
Please simply don't do it. Choose one "main" domain and setup 301 redirects from all other domains to the main one.
This allows you to fully use any wordpress template you wish to, without having to customize it for your main joomla template.