Write a tightly structured, highly polished, properly formatted script. Producers who buy screenplays online are typically those with lower budgets, but they will demand a certain level of professionalism.
Join a site that allows you to post your screenplay online. One of the best is Inktip. For a small fee, the site allows writers to post as little as a log line or as much as the entire script. Its newsletter goes out to producers, agents and managers, which helps spread the word about your product.
Use social media contacts to connect with producers, readers and other screenwriters. This essentially replaces the circle of contacts you would make if you lived in Los Angeles.
Write a solid log line about the screenplay. It must be a concise but compelling synopsis that sums up the screenplay in no more than three sentences. This is the line most readers will see. If there is nothing special about it, they will not bother to read anything more.
Keep up with online options from producers. On occasion, some will do an online "pitch fest" where they will listen to screenplay pitches in real time with online writers. Some also hold contests that can draw the attention of producers. Check moviebytes.com for updates on those contests.