Object Data in labels?

I have a table with Tax rates in it. When the user gets to the last screen, I'd like to show the tax rate in the label, beside the actual tax amount... Any way to do this?

So it would look like:

PST 6%: $4.25

With the 6 coming from the connected tax rate object...

Well, they seem to be so close.. They have the rename label in the view display rules.. But it doesn't seem to take an object value.. If it did, then it would work nicely... I could have do a view Display Rule as:

if PST.Rate is not blank then rename label of PST Rate to "{PST.Rate}% PST" in that field and all would work beautifully.

I can't use the display rules, since there will be different years at different rates for different places and the users will just be adding a new rate for a new year, and that wouldn't update the form/display rules..

If there aren't too many tax rates, then you could use Form/Display rules to set this up - unfortunately it doesn't seem to be possible to set a label to a formula result - only to a literal value so there would need to be a rule for each possible tax rate.

How about this Knack - being able to assign a formula to things like this?