Installing battens as spacers for new bargeboards

[hassl]

Hello,

I need to replace some fascia boards. I currently have 170x28, but it seems hard to find them anywhere so I might have to buy 170x22. There are 2 of them, so the delta becomes 12mm. Would it be possible to put 12mm battens on the inside there as a spacer to bring them out towards the fascia metal?

 

[fribygg]

Buy 34mm timber if you can't get 28, regular panel boards will be too flimsy.