Few things coming in my mind for the situation you are asking:-
If you have a dedicated mobile site then you might add a dedicated tag to that website and start collecting cookies so that those users are targeted separately using this tag.
You might go for custom combination option using various permutation and combinations which can be applied using the existing remarketing tags to target specific set of users. Find more details of how to create custom combination list here: https://support.google.com/adwords/answer/2549111
I hope that helps a bit!