Ok I figured it out. This probably isn't the most optimal but the only way I could figure out how to do it.
IfFileExists "$INSTDIR\adjuster.exe" 0 NoAdjuster
MessageBox MB_OKCANCEL|MB_ICONINFORMATION "Note: A previous installation of CableNut was detected.$\nIt is recommended you uninstall any previous version of CableNut before continuing." IDOK Instcont
FindWindowByTitle "close" "CableNut 4.02 Setup: Installing Files"
FindWindowByTitle "close" "CableNut 4.02 Setup"
Man I love that Nop