Manipulating the layout of an OO-document

Hi,

I'd like to know, if there is a way to implement a formating instruction in a php-variable-value, so that this formating instruction, like a font-size, is transformed into OO-Formating.

Example:
to fill [var.text]
I would normally prepare
    $text = "short_text";
in php. If I could, for a longer text, prepare
    $text = "<tbs font-size='8pt'>long_long_text</tbs>";
the the OO-document should be modified to display the long_long_text in the font-size specified.

As I understand, tbs does only work on the content.xml and modifications of the layout in the other sub-files is not done?

If I do have my head in the clouds here, get me down to earth.
Thanks in advance

Martin