HP DC7800 back panel replacement

I have a HP DC7800 that i bought a while back
and want to repurpose it by giving it a graphics upgrade with a HDMI output. I have a
spare low profile Nvidia GT520
graphics card that is compatible with the system
board and has the required HDMI i need for the
system. The problem is, the system i purchased
came with the full height PCI option so i am
unable to access the PCI-E slot i need for the
graphics card.
Is there a way i can replace the back panel that
has the PCI Riser with the back panel that has
the 4 Low profile slots accessible, and if so and if
at all possible, where can i get said back panel.
Thank You