Congrats to you and your work for others.
Yes, you can take a more northerly route - you just have to do more homework.
State Dept of Transportation website usually have traffic volume maps -
These give you a good idea about which roads are busier or quieter.
AADT - Average Annual Daily Traffic
Rough rule of thumb for me:
Under 500 - Serene
500 to 1000 - Nice
1000 to 2000 - OK but more caution used
2000 to 4000 - Getting busy, shoulder useful
Over 4000 - Really busy, shoulder essential
If you take COLO 52 east from Boulder almost to Wiggins -
You can pick up Avenue Q (paved) to Fort Morgan rather then the I-76 service road.
From there, US 6 makes for a nice ride all the way to Lincoln (bike friendly town)
[There are more remote and scenic routes - a little longer, using more back roads]http://apps.coloradodot.info/dataaccess/Traffic/index.cfm?fuseaction=TrafficMain&MenuType=Traffichttp://www.dor.state.ne.us/maps/Statewide%20Traffic%20Flow%20Maps/2010-Statewide-Traffic-Flow-Map.pdf
There is a spectacular, new bike/ped bridge across the Missouri in Omaha
But getting into Omaha can be a hassle.
An easier crossing is at Plattsmouth - narrow, but refurbished surface, and 25mph.
Iowa does not have many roads with shoulders.
They have a great cycling map which shows traffic on county roads.
You can take in the Bridges of Madison County and the college town of Iowa City.
[I will be glad to provide assistance]http://www.iowadot.gov/maps//msp/pdf/bikemappdf.html
The nicest bridge to cross the Mississippi is at Davenport/Rock Island - Centennial Bridge.
(Gotta use the north side sidewalk - south walk is blocked.)
Then you can ride 20 or so miles along a bike trail on the river.http://www.johnweeks.com/river_mississippi/pagesB/umissB07.html