I've practiced in Colorado as well. First of all your vertical bearing pressure has nothing to do with the lateral earth pressure. The bearing pressure is going to based on in-situ strength unless the house is placed on fill. The lateral earth pressure is based on dumping uncompacted backfill...
http://www.fhwa.dot.gov/engineering/geotech/library_listing.cfm
If you go to this site you can probably find a manual on what you're dealing with to download. I think I even saw some free public domain software on the site. I'm one of the authors on the Manual for Design and Construction...
Filling the pile won't increase the tip capacity. If anything the capacity will be lower because you are adding the weight of the concrete as a load. A closed end pile is just that closed at the driving end.