I have, and in general I've split two on 1 with the 1 player have double the points or something to that effect.
The other way to do it, rather than just free for all, is an objective based game (capture a person of interest, item of interest, or similar).
I have also done it with a search mission (multiple buildings, where players search them to find various items worth points).
In the objective based game, invariably folks will team up on the currently winning player, but once another player gets in the lead the team up will switch vs that player. Usually I run it so that the player has to get the objective off through their starting position, or take it to something specific (such as take it to a shrine and be the only model on the shrine for a whole activation for the controlling model)
In the search games I find players do not gang up unless there is a clear winner way out in the lead. Based on the players I use a modified card deck (one card for each house), with each card equating to some item. It might be points, it might be nothing, it might be a peril (such as a snake which the player either has to fight or survive an attack roll from), or it might be something useful (such as finding a teppo and ammo). Break the buildings up so folks will have to fight over them and split forces up. Then use the 'take a head' rule to add options to score, and at the end tally up points.
Here is the search game I've used a few times (3 and 4 player, and for both Ronin and FFoL):
https://leadadventureforum.com/index.php?topic=122078.msg1532328#msg1532328