On pull request 43, dblock had asked if it would be possible to release the already shipped version 1.5 to Maven. At the time, the best answer I had was an "I think so". Now that I've investigated, I believe the answer is "definitely". Here are my suggested steps to do so.
One-Time Setup (needed for any publishing to Maven Central, not just this process; particulars can be found in the Sonatype OSS Maven Repository Usage Guide):
1) Gain access to a repository to deploy to
2) Configure your repository credentials in settings.xml
3) Create a GPG key and publish it
4) Install Maven 3
Per Artifact Version to Publish (waffle-jna.jar version 1.5 used as an example):
1) Create a working directory for waffle-jna-1.5
2) Create a POM file for the version and put it in the directory as pom-1.5.xml
3) Put the main jar in the directory as waffle-jna-1.5.jar (I grabbed this from the release download)
4) Put the sources jar in the directory as waffle-jna-1.5-source.jar (after running the Ant build, I grabbed bin/waffle-jna-src.zip)
5) Put the javadoc jar in the directory as waffle-jna-1.5-javadoc.jar (after running the Ant build, I created this using the command "jar cfM waffle-jna-1.5-javadoc.jar -C waffle-jna/doc/ .")
6) Run the following command in the directory (substituting the appropriate REPOID and REPOURL), providing your GPG passphrase when prompted
mvn org.apache.maven.plugins:maven-gpg-plugin:1.4:sign-and-deploy-file -Dfile=waffle-jna-1.5.jar -DpomFile=pom-1.5.xml -Dsources=waffle-jna-1.5-sources.jar -Djavadoc=waffle-jna-1.5-javadoc.jar -DrepositoryId=REPOID -Durl=REPOURL
Step 6 uses the Maven gpg plugin to sign the 4 files (pom, jar, sources, javadoc) and upload them as a single step. I tested this on Bintray; the only difference with Sonatype OSS should be their requirements on POM files.
Here's the POM that I used for my testing.