We now routinely leave in the sitouts -obviously the tournament has to be 'timed' otherwise the sitout table never move. Replacing with named subs sometimes works, sometimes doesn't -error message is that it didn't work. Replacing with random subs has been a real headache, with subs often dropping out after a couple of boards and being repeatedly replaced. If less than seven tables, I change the movement to 15/18 boards, three board rounds at the last moment. This means pairs only sitout once, albeit for 24 mins, max. With two board rounds, pairs can sitout several times if you aren't careful. Maybe not standard practice, but it works for us -members are more willing to have a sitout than to play against random players who may, or may not, be friendly.