I wrote about OMR marks back in April - I made a passing comment about using MSWord shapes to put the 'slugs' onto the document. I thought I had written about that method previously - I hadn't!
Klaus put together an RTF a while back to demo this - I nagged him for it to support this post. He recreated it for us. The basics are to add a line shape to the RTF template where you need the marks.
Its a simple case of adding the line shapes to the document - positioning them might get a little tricky but remember you can change the units used in the document to something finer than Inches or Centimeters such as Points or Picas. Tools > Options > General > Measurement Units.
If you need to have the marks on every page, the key is to put the template into Header/Footer mode - View > Header/Footer. You can then add the 'slugs' where ever you need them on the document.
I have not tried it but if you need more dynamic placement of the slugs you could use the shape manipulation functionality we provide in the template. Check the user documentation or for a quick overview the shapes demo created by Jen in the Demo Catalog.
I have loaded Klaus' sample file here.