Kindly refer to the Programming specification
On page 7, Figure 2-1, you will find the minimum required connections for the end product to support ISSP. You can kindly substitute MiniProg for Host System. All that is needed to two power supply pins and two GPIO pins and a reset pin.
You can make a small PCB with the required five connections to MiniProg, as shown in the diagram mentioned earlier. You can even use a ZIF socket in this PCB, which can make it safe and easy to mount and unmount the devices for programming.
You can also use third party device programmers to program CY8C29866-24AXI 100TQFP. You might need to purchase a 100TQFP adapter separately. Kindly follow the column "PSoC1".