let me guess, by seeding a torrent?
Go to settings --> network and set up your connection with the custom setting. Select automatic on everything but when you get to MTU, select manual and set it to 900. Keep going until you get to test internet connection and then just back out.
Keep in mind though, this keeps people from entering your session at all and if they do enter, they almost always tend to leave 95% of the time so don't do large sales with your friends in a lobby like this.
Rather, invite them, leave and change your MTU back to the default setting (usually 1500 and you can set this manually too) and then join back on your friend. The public lobby is normal then and it's only you two in there. People can still join this way though and stay but this way you at least have a good solo lobby to begin with.
Another way is to lag out a lobby using the change date/time method but that never seems to work for me, making my game crash instead. You can try it though, it's different for everyone.