If there is already an existing pom and want it to be deployed together with the 3rd party artifact, set the pomFile parameter to the path of the pom.xml.
mvn deploy:deploy-file -Durl=file:///C:/m2-repo \
-DrepositoryId=some.id \
-Dfile=path-to-your-artifact-jar \
-DpomFile=path-to-your-pom.xml
Note that the groupId, artifactId, version and packaging informations are automatically retrieved from the given pom.