Best way to resolve a tie in this Swiss-system tournament situation?

I recently ran a Swiss style tournament for high school kids. After 5 rounds, there was a tie for 3rd place with 3.5 points. They had played each other and got a draw. Players in the tournament did not have official chess ratings. I told them at the beginning of the tourney that if this happened we would calculate the cumulative score of their opponents. Since we had an odd number of players, one of the two kids had gotten a bye. For the bye round, should that be counted as an opponent with a score of 0, 2.5 (the average score), or something else? They wanted an official third place winner, and I had to make a decision on the spot, so I gave it to the kid who had actually beaten 3 opponents without getting a bye. If I would've treated the bye round as an opponent with 2.5 points, the other kid would've gotten it through cumulative opponent score. What was the best way to resolve this? Thanks in advance.

The most common tiebreaks for the big NYC scholastics are MSCO.

In order:

Modified Median

Solkoff

Cumulative

Opponents' Cumulative