[Internal Supports??]

I'm struggling on what to even call what I'm looking for I would consider it an internal support but it is on the infill section of the part. I have a low infill density and sections of the part start out floating in mid air. I know the easy way to fix this is to bump up the infill but on a part this size that increases the print time and is really just wasting filament . Is there a way to add support or extra infill in certain regions of a part without just increasing overall infill density. I've attached a couple pictures that hopefully help explain what I need.

 

Thanks 

 

Scot