How to increase carrying capacity?
 

I'm trying to add Bearfolk, from the Midgard campaign setting.

One of their abilities is that they treat their Strength as 5 points higher than it is, *for their carrying capacity, maximum lifting, and dragging weight*.

It has no effect on other damage, attack rolls, etc.

It also doesn't stack with any spell that or item that increases the bearfolk's strength.

How would I stat this out? I can borrow part of the script from Muleback Cords, I think. But what about this part:

It also doesn't stack with any spell that or item that increases the bearfolk's strength.