1) Hook your humidifier up to a length of rubber hose and run it to the drain in your basement (if you have one)
2) Keep your basement door closed and put a rubber flap on the bottom of it so that it makes a good seal. This prevents the heavy moist air from sinking into the basement. At the same time, block off all air register vents in the basement to prevent the upstairs air from go through them.
3) Sometime a fan or two in the basement helps so the moist air doesn't pool in certain areas and cause mildew/mold growth.
4) Get a second or a bigger dehumidifier
The harder stuff
1) Seal up the top of the cinder blocks where it meets the upper part of your house with some of that expandable insulation foam (if it's a big gap) or so caulking ( if it's a smaller gap).
2) Make sure the cinderblock's mortar is in good shape (ie: no holes or cracks). Repair if required.
3) You can parge the interior wall with a moisture sealant-type cement mixture.