The trivial option would be to do a full clone and delete contacts via GUI afterwards - but that would have to be in chunks of 100 (unless you do a little tweaking in the browser - not user-friendly) , and may thus be heavy work.
The only other options I can think of require being comfortable with database manipulation, plus understanding Mautic’s database structure. Basically: Empty all tables that refer to contacts (“leads”) via “lead_id”.
One could do that after import, in the new instance.
Or one could have a little export script that does this for you during export.
-> I’d suggest find someone to create that script for you (and open source it : )