When it comes to counter weight, you pretty much have 3 choices. You can fill the tires but that is not enough to properly ballast most machines. Next you can add wheel weights (read NOT cheap) or you can mount an impliment on the 3 point hitch such as a beefy box blade or landscaping rake. If you want to keep the 3 point hitch open then you are pretty much relegated to wheel weights.
One other option which may help out some and I am going under the presumption that you have R-1 ag tires mounted on your tractor. If your dealer will trade out with you, you can have a set of the large R-4 industrial tires mounted and fill them. They hold a larger volume of fluid and thus more weight but they have draw backs in mud and gooey conditions and don't get as good a traction as R-1 ag tires.
The last outside option is to have the operator of the machine start eating real good to put on some weight.
I provide about 240 lbs. of ballast weight when I am in the seat.