Not as difficult as some may think. Have a register that peoples names are entered that deposit. The sum has to stay from one season to the start of the next. Interest hasn't got to be paid in money. If say a ticket holder deposits £1000 then the following season he receives a discount of £30 off the cost of his season ticket i.e. 3%. No tax no fees no trouble. If some one deposits £100 then he gets the equivalent of three pound i.e. a free pint.
In an ideal situation say 600 bought season tickets and each deposited a £1000 then the club would have £600,000 to negotiate with. The money is still the supporters and he/she is receiving the interest on it. Of course there are many variations on any scheme. But, it is a thought.