Our small company currently offers no benefits to employees. During the interim period before we create a plan for everyone, can we offer to reimburse medical expenses / insurance for one exec?

If you are not trying to have the reimbursements excluded from taxable compensation, you have no problem. You can pay employees whatever you want, subject to the excessive compensation rules.

If you are thinking about nontaxable reimbursements, start with section 105(h) of the tax code.

thanks, that's helpful. It looks like the nondiscrimination rules would apply and the reimbursement would be taxable.