Allow price rule / voucher to count towards shipping cost

[ShaunJUK]

So basically I sell Gift Cards in my shop using a module however the module just generates a price rule. This is fantastic however it means that if someone has paid £20 for a voucher they can't obtain products and shipping up to £20 using the voucher as the voucher doesn't count towards the shipping.

Is there any way to make the voucher code reduce both the goods and shipping by the amount of the voucher?

I hope that makes sense.

Thanks