If you do a search on these forums for 'Haltech F5' you'll find several threads about that a Haltech controller that does just that - it controls an additional injector which you can place in the intake to provide extra fuel to the engine at a certain boost level. This is an unsophisticated system and people don't favour this way of injecting extra fuel for a reason. The reason generally circles around the reasoning that it doesn't effectively distribute the extra fuel to all the cylinders (especially in the case of the standard intake manifold). Several people have successfully run the 5th injector setup with the additonal injector tapped into the throttlebody. I'm not saying don't do it, but if you're already looking at ways to cheaply turbo a CG13, a long way down the line you'll end up realising it costs you more in the long run once you start having problems because no one's ever used that particular combination before.
Find a tuner in your area - ask him what ECUs he tunes and then use that. There's no point in getting something outlandish, whether it be cheap or super-expensive, if no one knows how the **** to tune it properly.
Do a lot of forum searches, particularly in the forced induction section if you're keen on actually following through with a turbo setup.
---dens