In any case, i realized it could not be done. So I installed custom fonts in my heroku machine using an extremely smart solution I found here: www.mobalean.com/blog/2011/08/02/pdf-generation-and-heroku
Code as follows. Hope this would be useful for anyone who needs custom fonts in heroku/wkthtmltoimage
if Rails.env.production? || Rails.env.staging?
font_dir = File.join(Dir.home, ".fonts")
Dir.mkdir(font_dir) unless Dir.exists?(font_dir)
Dir.glob(Rails.root.join("vendor", "fonts", "*")).each do |font|
target = File.join(font_dir, File.basename(font))
File.symlink(font, target) unless File.exists?(target)
end
end