Is there any way to run apps made for 3gs and higher on a 3g? A way to perhaps fake the app into thinking you're on a 3gs or even installing a custom 3gs ios on the 3g itself.
Believe me I know the apps would run poorly on an underpowered 3g but Im curious to try.
Even if possible, it would like you said run poorly. The hardware just isn't suitable. It may seem like something that people believe they "can deal with" but honestly the performance is seriously poor.
Example: psx4all on a 3GS will run well, on an iPhone 4 it will run amazingly. On an 3G (I've done this myself) it is nearly unusable. The introduction of a game doesn't simply lag, it drags along. A 1 minute intro can take probably 15 minutes to play. I'd assume this type of performance can apply to other apps as well.
Probably better to just get a 3GS or not use an app that requires better hardware.