Installing RTC client to Flex 3 Builder embedded Eclipse

We have a problem similar to post "installing RTC to two locations on same physical machine". The difference is the 2nd install target is an Adobe Flex 3 Builder which has its own bundled Eclipse. This Eclipse appears to not have all the normal Eclipse directories (e.g. plug-ins). The Flex Eclipse version is 3.3.1.R33. The first error we get on an RTC install, is The platform configuration of the existing Eclipse installation is not initalized. Missing file "c:\Program Files\Adobe\Flex Builder 3\configuration\org.eclipse.update\platform.xml". The Flex 'configuration' directory contains a single file of "config.ini", as opposed to all the files and directories in a normal Eclipse. I tried to copy some of the normal Eclipse directories over the Flex Eclipse, and did succeed in getting the RTC install to get further, but was concerned about doing this kind of thing, so stopped.