Ummm.... I fail to believe that the pie plate wheels OR the spoiler have any real affect on CoD. It's purely an aestetic thing. The Si spoiler certainly is not intended to add more downforce to a FWD car... It's for looks.
Once you remove the OE spoiler, you could plug the holes rather cheaply with any kind of body filler or epoxy. No need to do a real clean job as the OE holes would be covered by the bigger Si Spoiler.
You will have to DRILL holes in your rear trunk to get the Si spoiler installed though.
https://www.hondapartsdeals.com/hond...ponent=B++5510
FWIW, you can also insatll the Si front grill. It's a direct bolt on.
http://www.collegehillshonda.com/hon...c_exterior.htm
I'm going to relocate my Hybrid emblem to the front grill, in place of the "Si" emblem...