Hi @wietseneven
This is possible, but will not be an easy task.
Creating your own field type is quite easy. Here is a link to get you started:
http://www.advancedcustomfields.com/resources/tutorials/creating-a-new-field-type/
What you need to do is either create a new field type which has 2 select fields, or just use 2 normal select fields to hold the data.
You can set the default choices to nothing which will give you blank select fields to work with.
Then, you can use jQuery to populate the select fields on load and when a change is detected on the select?
Does that help?
