You need to modify AppController.mm and check for an iPhone 4S in the CreateSurface code, changing the returned resolution if you discover that it is an iPhone4 or less:

bool CreateSurface(EAGLView *view, EAGLSurfaceDesc* surface)
{
    CAEAGLLayer* eaglLayer = (CAEAGLLayer*)surface->eaglLayer;
    assert(eaglLayer == [view layer]);

    CGSize newSize = [eaglLayer bounds].size;
    newSize.width  = roundf(newSize.width);
    newSize.height = roundf(newSize.height);

#ifdef __IPHONE_4_0
    int resolution = UnityGetTargetResolution();

    // Start modification //

    if([[machineName() substringWithRange:NSMakeRange(0, 6)] isEqualToString:@"iPhone"] && [[machineName() substringWithRange:NSMakeRange(6,1)] compare:@"4"] == NSOrderedAscending)
    {
        resolution = kTargetResolutionStandard;
    }

    //  End modification  //


    if (    (resolution == kTargetResolutionNative || resolution == kTargetResolutionHD)
         && [view respondsToSelector:@selector(setContentScaleFactor:)]
         && [[UIScreen mainScreen] respondsToSelector:@selector(scale)]
       )
    {
            CGFloat scaleFactor = [UIScreen mainScreen].scale;
            [view setContentScaleFactor:scaleFactor];
            newSize.width = roundf(newSize.width * scaleFactor);
            newSize.height = roundf(newSize.height * scaleFactor);
            UnitySetInputScaleFactor(scaleFactor);
    }
#endif

    surface->w = newSize.width;
    surface->h = newSize.height;

    UNITY_DBG_LOG ("CreateWindowSurface: FBO\n");
    CreateSurfaceGLES(surface);
    GLES_CHK( glBindRenderbufferOES(GL_RENDERBUFFER_OES, surface->renderbuffer) );

    QCARUnityPlayer::getInstance().QCARNotifyCreated((int)surface->w, (int)surface->h);
    return true;
}

Then add this code to the top of the file:

#import <sys/utsname.h>

NSString*
machineName()
{
    struct utsname systemInfo;
    uname(&systemInfo);

    return [NSString stringWithCString:systemInfo.machine
                              encoding:NSUTF8StringEncoding];
}