Take a plastic zip top bag, and put it inside a pint glass or tall quart size container. Fold the top of the bag down over the outside of the mug/container. Essentially, you're just using the mug to hold the bag up and open.
After you've melted your chocolate, dump it into the bag, squeeze out extra air, and zip the top closed. You've got a single use pastry bag!
Edit: Adding a suggestion from Graham: You can melt your chocolate directly in the zip top bag by placing your chocolate pieces in the bag, then placing that bag directly in your water bath to melt--thus saving the entire "transfer messy, warm, gooey chocolate into a zip top bag" step entirely.
Nearly all freezer zip top bags will happily survive the water bath. Thinner, or budget bags may not keep together at the seams as well when heated, so read the box, or test first by filling the bag with plain water & heating. This way you can test durability without wasting a batch of chocolate.
Hold the bag with one corner pointing down. Use one hand to hold the bag on the top, so that squeezing will push the chocolate down (like a pastry bag). Now clip that corner off the bag with scissors. You can now drizzle in a nice steady stream, giving a squeeze, pushing chocolate down as you go.
With some practice, you'll be able to get a very even netting. And if you do it often, you can graduate to a proper pastry bag eventually, which makes things even a bit easier.
For a more detailed set of instructions with photos (albeit with a proper piping bag, but it's the same process), check out this.