Looks like we can't use the Installation Manager, but I did get these instructions that might help others:

To manually add TeamConcert to an existing Eclipse install start by extracting the contents of the TeamConcert zip file.
When this is done there will be a directory structure that looks like this: (I can't post this image here but have listed the directories needed below)

Highlighted directories (subdirectories of \jazz\client\eclipse)
\dtp
\emf
\gef
\jazz
\links



The way that the TeamConcert client is built we start from an Eclipse platform build and add the jazz specific code and code from several other eclipse projects. Each of these contributions is in their own directory and we use the "links" directory to tell the Eclipse runtime where it needs to look for all of the necessary plugins and features. If your target Eclipse already contains one or more of the non jazz plugins (e.g. dtp, emf, gef) the steps are a bit more complicated and I'll cover that later.

If the Eclipse instance you want to add TeamConcert to has only the Eclipse SDK you just need to:

1) Copy the directories that I highlighted to the target Eclipse
2) Merge the contents of TeamConcert.ini with Eclipse.ini. The key settings are the memory options and jit flags.
-vmargs
-Xms100m
-Xmx300m
-Xjit:exclude={com/ibm/team/coverage/internal/common/report/SourceElementInfo.write*}
-Dosgi.requiredJavaVersion=1.5
-
You should copy the teamconcert.ini file as well. In this particular case it was renamed to eclipse.ini since there were no interesting settings that were needed to merge.

Once you have copied the files you need to flush the OSGi caches. This can be done by passing the -initialize flag to eclipse.exe once
eclipse.exe -initialize
You should be all set to go and can run your existing eclipse with TeamConcert.

If your target Eclipse already contains one or more of the non jazz plugins (e.g. dtp, emf, gef), then depending on what additional plugins you have installed into your Eclipse
you may already have some or all of these additional Eclipse plugins. For TeamConcert we only include the plugins that we need from these other Eclipse projects so there may be some additional work required. The strategy that I would suggest is to start by only bringing over the jazz directory and the one link file that will add our plugins and only add the
code from the other projects if a required plugin isn't found.

Placed this in a document, and added to work item here:

https://jazz.net/jazz/web/projects/Jazz%20Project#action=com.ibm.team.workitem.viewWorkItem&id=49703

Excellent - thanks James.