This used to work, I think the only change needed is to make tthe dependency to org.eclipse.pde.launching optional.

Cannot complete the install because one or more required items could not be found.
  Software being installed: Scala IDE for Eclipse dev support 4.4.0.local-2_11-201602291023-01a4691 (org.scala-ide.sdt.dev.feature.feature.group 4.4.0.local-2_11-201602291023-01a4691)
  Missing requirement: Scala Debug Plugin (Test) 4.4.0.local-2_11-201602291023-01a4691 (org.scala-ide.sdt.debug.tests 4.4.0.local-2_11-201602291023-01a4691) requires 'bundle org.eclipse.pde.launching [3.6.0,4.0.0)' but it could not be found
  Cannot satisfy dependency:
    From: Scala IDE for Eclipse dev support 4.4.0.local-2_11-201602291023-01a4691 (org.scala-ide.sdt.dev.feature.feature.group 4.4.0.local-2_11-201602291023-01a4691)
    To: org.scala-ide.sdt.debug.tests [4.4.0.local-2_11-201602291023-01a4691]