So, you can buy an extra buck converter^ and solder it yourself --removing additional resistors on the PCB-- and it still won't be 802.3af/at compliant, or you can just buy a proper PoE adaptor for $10. [0]
^ Please show me a buck converter that does 48VDC->5VDC for "a few bucks"
[0] http://www.tp-link.com/us/products/details/TL-POE10R.html