Actually ACE2-Spike protein interaction should be targeted for developing a peptide/chemotherapeutic. Apart from its involvement in binding SARS-CoV-2, ACE2 plays important physiological role. Therefore, antagonist against this receptor may hamper physiological homeostasis, especially regulation of blood pressure.

The physiological function of ACE-2 is the maturation of angiotensin , So blocking the catalytic site of ACE-2 will not be favorable (it will have cardiovascular implications) . So if your question is whether ACE-2 inhbitory peptides can be useful for blocking SARS-CoV-2 entry, my answer will be 'it might not, but it will definitely have serious side effects'.

However , if you look at the structure(PDB:6M17) , the peptidase domain of ACE-2 has two distinct lobes mediating the substrate engagement. The RBD -ACE-2 binding interface includes one of these lobes , but it does not block the active site. The spike interaction interface of ACE-2 is quite distinct from its active site .

So one of the options to block the interaction will be to use a peptide derived from the α1 helix of ACE2,which will very well be able to bind to spike and block the virus from entering the cell. Here are some interesting reads:

https://www.biorxiv.org/content/10.1101/2020.03.19.999318v1

https://blogs.sciencemag.org/pipeline/archives/2020/04/20/good-news-on-the-coronavirus-angiotensin-connection

The S protein of SARS-CoV-2 exists in the form of a trimer. Each monomer contains approximately 1,300 amino acids, of which more than 300 amino acids constitute the "receptor binding domain" (RBD), where the S protein is bound to ACE2 . Read more at https://www.cusabio.com/c-20982.html