In short, no.
This used to be a grey area in the tax code (although there were always potential issues with the Department of Labor). But recent rulings from the IRS and the DOL have made it very clear that this cannot be done on any sort of pre-tax basis.
Potential penalties? $36,500. Per year. Per employee.
And the use of a Health Reimbursement Arrangement (HRA) to reimburse premiums tax-free? Also no good.