No you don't. Just cut off payment of indirects on all Federal grants, and the campus police will have all the illegals rounded up and delivered to the train station in about ten minutes.
If by all Federal Grants, you mean including Research Grants, than yes that along with suspension of other Federal Aid will be an eye opener. In FY2014 (Can’t find anything more recent), Harvard was awarded $609M in federal grants. It also submitted requests for an additional $2.8B in grants.