to add custom chars to the font, you have to find the correct font.
The header uses the Milford font (
http://www.fontspace.com/roger-white/milford)
i don't know exactly which is used in the demo, but try your way.
goto
http://cufon.shoqolate.com/generate/ and select the font you would like to convert to a .js file - note you can have 4 different fonts in one .js file e.g a regular, a italic, a bold, and a italic/bold.
check the box ; The EULAs of these fonts allow Web Embedding (without Adobe Flash)
scroll down to the textbox ".. and also these single characters" and enter which chars you want to use beside the basic latin.
scroll down to the very end and check the box " I acknowledge and accept these terms" and then hit Let's do this!
then upload the font to the templates/gk_coperate2/fonts (DONT RENAME IT !!!), and then go to your admin page and into extentions > template manager > gk_corporate2 > fonts > and choose the new font and in the cufon fontname header write the name of the font without the 400/700.font.js. see the screenshot below...