Answer
With those specific constraints (no saved search, no template/profile-based approach), filtering a standard field's LOV this way isn't achievable without a genuine modification. Two realistic paths: the safer, non-invasive option is to lean on saved searches and base profiles to deliver the filtered experience to end users without touching the standard LOV itself — this is generally the recommended approach since it survives upgrades cleanly. The alternative is a real modification: if your release has a 'Hide from LOV' capability on the relevant basic data, add a custom flag for it and adjust the affected views to respect that flag — but treat this as a genuine customization that needs to be reviewed and potentially reworked at each upgrade, not a configuration-level change.