How to random assign subjects to a group without any equipment?
If the patient has given you some kind of ID number (soc#, drivers license, patient number, birthday month... most any number) just split by even/odd. 

If we assume that such numbers are sequential or randomly assigned, then there should be no large bias, or association with any patient characteristics.

If you have two or more numbers available, you could add the last digits and see if that is even or odd.