Ok, I just spent a good 1hr 40mins killing 3 dummies as suggested in the original post.
I am wondering if the kills have counted towards Seriously or not though. I started the match with 3v3 players. Upon the game starting I minimized the game and removed the 2 players from my team (to make it playable), thus making it 1v3 -- me versus 3 dummies in Ranked.
I got exactly 806 kills after 1h 40min session, captured the hill in Annex to end the game. I was satisfied it had worked, that is until I checked the Versus Leaderboard (Annex; All Time) and my kills in Annex DID NOT go up at all from that match.
Is it possible it has still counted towards Seriously, and maybe just Gears PC practically being dead, the Leaderboards may just not get updated anymore -- or so I am hoping.
Anyone know for sure either way?