account_location and domain forwarding

i'm playing around with an idea i had for using a rails app with
multiple domains. i used the account_location plugin which works
great.

however, eventually i would like to do something similar to shopify
where they allow you to add dns entries to your own domain and forward
it to the subdomain on their site. for instance, i could have
mystore.myshopify.com and add a cname record so that shop.mydomain.com
would point to that, or even a top level domain like mydomain.com.

i'm not very knowledgeable when it comes to dns, so i don't know how
it works. but is there a way to set the account_location plugin to
handle something like that or would i have to do some sort of dns
lookup to make sure the requesting domain matches an account that's
set up?