We could have embedded the font ourselves but we had some legal issues with the font so we decided to use the font without embedding it. I believe users that do not have the Segoe would just fallback to the default Silverlight font.
Recompiling the Metro theme would be an option but I am not sure the Metro theme solution we have distributed with the last service pack is suitable for that. Its Style files are placed in the bin folder which is obviously a problem since they should be in the themes folder. We are working on that now but we will be able to ship the theme project as early as the next ServicePack or Q3.
If I were you I would not bother embedding the font and just left the users that do not have the font experience the default Silverlight font. As for the font sizes I believe you could still get the Metro theme styles from the installation folder:
C:\Program Files (x86)\Telerik\RadControls for Silverlight Q2 2011\Themes\Metro\bin\Silverlight\4.0\Release\Themes\Metro\*.xaml
(note that the installation path may differ)
Add the styles in your projects for the controls that differ from your application the most and hardcode the FontSizes in the ControlTemplates.
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