Mobile Radiobutton Likert Scale design for comparing a variation

We want to know/measure if users prefer variation A over variation B. Therefor we run an paired comparison experiment that needs to be completed on a mobile phone.

They will see/experience two variations after which they have pick one, and then rate the concepts on two aspects.

The problem we have now is how to display a seven point radiobutton rating scale on mobile, in which there is not much space for labels. It should be suitable for iphone 5 and bigger.

Match with ....

A 0 | 0 | 0 | 0 | 0 | 0 |0 B

We need to communicate that this is scale that goes from A is better to B is better.

What we considered: Color coding, one label on both ends.

I could not find a standard solution for this.