You can probably use the same method I use for scribing styrene. You need some Dymo tape (the tape used in the Dymo label embossers - big in the '70's, but still available) and a sewing needle chucked in a pinvise.
Lay out the tape in the pattern you want to scribe the lines. Then using the needle in the vise, follow along the tape. Start with light pressure at first, then increase it as you develop the line.
The reason I use the Dymo tape is that is fairly thick and sturdy, so it acts as an flexible guide ruler. And because of the adhesiveness, it doesn't slide around while you're trying to work.
You can also pick up specialty engraving tools (the one from missionmodels.com is great), but they can be a bit pricey.
-Fred