How do I manually integrate the GCC toolchain into e2 Studio and SSP?

You can manually integrate the GNU ARM toolchain manually by following the below steps: 

1) Within e² studio Preferences (available via Window> Preferences), select C/C++ / Renesas / Renesas Toolchain Management and then manually point e2 studio to the location of the GNU ARM Toolchain (as shown in the screen capture below:

2) Click Add and you get an Add New Toolchain window (as seen below):

3) Put in the location of the Toolchain Path and click OK. The toolchain will be added and should then be integrated into e2 studio.