Congregants or regular visitors to churches with sanctuary rails know the drill:  If you cannot kneel or have bad knees, don't kneel.  Receive communion over the rail while standing.  And if you cannot get there a priest or someone else will come to you in the pew.

Everyone knows how it works and nobody gets even the side eye or a nasty look.

This is the "merciful" practice.  Allow the people their piety, encourage and facilitate it, but do not exclude the disabled or presume that they are not genuflecting in their hearts.