Did you try adding a string in the certificate/lang/certificate.php file, then using that in the cert_printtext line?
I think that should work. Seem to vaguely remember that problem when I first played with certificate. What is the space character?   is what it is in HTML. Put each word in quotes then the space character between.
The other solution is to create 3 lines of code instead of 1, then you can control the positon of each word
Sorry I could not be more help. Try creating the string.