2 things:
1) My previous lab had nice rotovaps with good seals, so we could use those to drive off DMF, but we had to heat the bath to 60 or so to get it to pull off at a reasonable rate. If your rotovap isn't as nice, you may not be able to do this.
2) Do a vacuum distillation of the solvent. Set up a short path column, cool the collection flask to -78, then hit the vacuum. You can periodically warm up the solvent by holding the flask in your hand. Depending on the amount of DMF you have, you should be able to get this distilled out relatively quickly.