If you care overly much about balance in ability scores you shouldn't use dice to determine them. The standard array and point buy systems exist for precisely this reason. I would recommend getting your DM to switch your entire party to point buy and move on from there.
Both of these methods can be found in the PHB on pp.12-13
27 points to spend, all stats start at 8. Stats can not be reduced below 8, or raised above 15.
Preset stat distribution of 15, 14, 13, 12, 10, 8. Player picks where to put the stats.
Racial modifiers apply after these stats are put in place, ensuring no player is at or above 18 at level 1. This will ensure characters are all within a specific range, and no player will completely outstrip the others by virtue of good or poor luck alone.
An Alternative Solution
If you don't want to force the player who rolled really well to reduce his attributes the obvious alternative is to increase the attributes of the rest of the party. Allowing them to use whatever the best set of scores was is a perfectly viable solution, although it is a non-trivial power boost to the party. This is particularly true at early levels, when the additional bonuses from having a high ability score will have a larger impact on whatever the character is trying to do. A whole party full of high ability scores will probably require some balancing work on the DM's part, at least during early levels of the game.