At the end of the day season ticket holders are garunteed atleast one ticket. Those wanting a second i suspect many could be for young uns, relatives simple suggestion walk through your turnstile with your partner, kid, relative, friend give your match voucher and at the same time point out to the turnstile operator that he or she is also paying for this person that way that individual gets a voucher.
If it turns out before hand season ticket holders are getting two problem solved but that paying customer gets a voucher they could pass on anyway.