If I'm not wrong, the manifest file that the "XP look'n'feel" plugin creates, is saved in the build folder you define for your project (the folder used for the output filename in your project properties).
In any case, you could use an standar manifest that works for all of your Windows XP/Vista applications, and you could embed that manifest in your executable using resource (.rc) files, so you don't need to distribute the manifest itself with your program.
Here you have the two files needed:
generic.Manifest:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<assemblyIdentity
version="1.0.0.0"
processorArchitecture="x86"
name="Controls"
type="win32"
/>
<description>wxMSW application</description>
<dependency>
<dependentAssembly>
<assemblyIdentity
type="win32"
name="Microsoft.Windows.Common-Controls"
version="6.0.0.0"
processorArchitecture="x86"
publicKeyToken="6595b64144ccf1df"
language="*"
/>
</dependentAssembly>
</dependency>
</assembly>
generic.rc:
//////////////////////////////////////////////////////////////////////////////
//
// Archivo Manifest genérico para Windows XP/Vista
//
#if !defined(wxUSE_NO_MANIFEST) || (wxUSE_NO_MANIFEST == 0)
#if !defined(WX_MSC_FULL_VER) || WX_MSC_FULL_VER < 140040130
// ver la página sobre "isolated applications" en MSDN
#
#ifdef ISOLATION_AWARE_ENABLED
#define APP_MANIFEST 2
#else
#define APP_MANIFEST 1
#endif
#define RT_MANIFEST 24
APP_MANIFEST RT_MANIFEST generic.Manifest
#endif // !defined(WX_MSC_FULL_VER) || WX_MSC_FULL_VER < 140040130
#endif // !defined(wxUSE_NO_MANIFEST) || (wxUSE_NO_MANIFEST == 0)
The only thing you need is to add the 'generic.rc' file to your project target including it when compiling/linking.
Regards.