They make drive bay (5-1/4") intake fan items you know. As for putting something below those drives, is there room behind the face for a fan? How about in the drive bays? If there's screw holes for a fan, then there should be a way for air to reach it. If the bottom of the front/face has a slot, or gap, between it and the metal, then that's where air would get sucked in. It should, also, have fan mounting holes towards the bottom. If not, then you might try putting a fan on either side panel to pull air in. You can figure out where on either side (a right hand side fan would be different) and just drill mounting holes and cut a blow (or suck as the case may be) hole. You can put a fan filter on the other side of the fan (inside if you keep it all in) to keep the dust level under control inside the case.
Are you looking to get the case temps down, or the processor temps down?