It's much easier than that.
First of all, create part and assembly templates with the fields you would like to populate the title block with: Designer, DesignDate, TitleLine1, TitleLine2, DrawingNumber, etc. No spaces in the names.
Next, edit your sheet format. Add an annotation in the position you would like the field to be filled, font size and style as appropriate (do not add text to the annotation yet). In the annotions dialogue box, click the Link Custom Properties button (looks like a folder with a chainlink on it). In the Link to Property dialogue box, click on the check box for "external model reference" and then type your custom property name as created in the part/assembly templates in the Property Name field. Click OK twice and bingo!
Save the sheet format and drawing template. Insert a part or assembly that has the custom properties defined and watch the title block magically update.