To me, it doesn't really prove they can open the pdf file even though we show them where to download it if the software is not on their PC.
You are exactly right. ESIGN grants an e-delivery "license" to you and any consumer who is willing
and can demonstrate (prove beyond any question) that s/he
"...can access information in the electronic form that will be used to provide the information that is the subject of the consent." Notice that ESIGN focuses on the information contained in the document, not the document itself.
As you indicate, you're one step short of passing the ESIGN test. You will not obtain an ESIGN "license" unless you require the e-delivery candidate to open a sample statement and report at least one bit of information contained in the document. My preference is to place a dummy statement in the same location where the real ones will be located. In order to pass the ESIGN test, your customer will need to open the dummy statement and then respond to a test question--something like "what APY is shown on the test statement?"