import scala.util.Properties.propOrEmpty

import com.typesafe.sbt.SbtPgp.PgpKeys._
import sbtrelease.ReleasePlugin._
import sbtrelease.ReleasePlugin.ReleaseKeys._

object Release {

  lazy val settings = releaseSettings ++ Seq(
    crossBuild := false,
    publishArtifactsAction := publishSigned.value,
    releaseVersion := { _ => propOrEmpty("releaseVersion")},
    nextVersion := { _ => propOrEmpty("developmentVersion")}
  )

}

import com.typesafe.sbt.SbtPgp.PgpKeys._
import sbtrelease.ReleasePlugin._
import sbtrelease.ReleasePlugin.ReleaseKeys._

object Release {

  lazy val settings = releaseSettings ++ Seq(
    crossBuild := false,
    publishArtifactsAction := publishSigned.value
  )

}

--- 
+++ 
@@ -1,3 +1,5 @@
+import scala.util.Properties.propOrEmpty
+
 import com.typesafe.sbt.SbtPgp.PgpKeys._
 import sbtrelease.ReleasePlugin._
 import sbtrelease.ReleasePlugin.ReleaseKeys._
@@ -6,7 +8,9 @@
 
   lazy val settings = releaseSettings ++ Seq(
     crossBuild := false,
-    publishArtifactsAction := publishSigned.value
+    publishArtifactsAction := publishSigned.value,
+    releaseVersion := { _ => propOrEmpty("releaseVersion")},
+    nextVersion := { _ => propOrEmpty("developmentVersion")}
   )
 
 }
Add possibility to pass release info as sys props
