Instance scaling in geometry nodes

I tried to replicate Default cube tutorial on geo nodes and built on it with drivers to make it mine. the next screen shot shows the original nodes to scale with attribut variable in the point scale node.

I’d like to be able to scale on 2 axis only using the “vector” option but using the variable “zscale” in the attribute node.

Is it a no go? is there a way to do it “my way”?
another idea?

simple enough… attribute separation and combine (with z being assign to a float fixed number (ie 1))