Well not exactly, at least how I set up a double that was a triple. Although some might disagree.
I start out “about” where I would set it as if the outer chainring was still there, which means you’ll have a lot larger gap between the 38t and the front derailleur cage.
What I want is to line the derailleur plates at the best position to shift from the 28t to the 38t and back again. If I am concerned I’ll drop a chain, I usually install a chainguard in the outer position. I’ve only done that on mtb’s.
It may take some tweaking, but it has worked well for me.
John