it is all in the timing
Here is what you are currently doing:
Let's say you sell a $100 GC and are in the 25% tax bracket.
If you claim the sale tomorrow, you owe uncle sam $25 and have $75 in hand which you are free to invest and earn $3 over the next year. On this same day next year, the client comes in and your employee gives the massage. You pay $50 to the employee, which is a loss since you have no income from that client this year, which reduces your tax burden by $12.50
But at the end of the year, you have $103 in income, $50 in expense and paid a net $13.25 in taxes, with a grand profit of $39.75. but you only have the use of $75 over the course of the year because you pre-paid your taxes by claiming it as 100% profit at the time of the sale.
Here is a better way
You don't claim the sale this year, because what you sold was a "promise" of a massage. You have $100 in your account. Financially, your balance sheet went up in the asset column (cash) and up in the liability side (IOU a massage WORTH $100). So all is right in the world. You owe no taxes on the $100. The $100 can earn you $4 over the next year.
$104 - 50 - $13.50 in taxes = $40.50 in profit. You also gained the use of that extra $25 for a year. $.75 in extra profit and the use of $25 for a year may not sound like much, but if you sell 20 GCs for the holidays that means you have an extra $515 in your bank account to help carry you through the slow times.
There is no additional work - you have to account for it some way.
If a GC expires unredeemed, the math is the same, except you don't have the $50 expense of providing the service.