If the issue is getting cables out of the way of the handlebar bag, a few options:
Cable housing under bar tape (use quality frictionless housing, as has been mentioned)
DT shifters
Any STI with cable routing under the bar tape
Convert existing bar ends to thumbies (but the mounts from Paul and other companies are nearly as expensive as new shifters)
Wireless electronic shifting
I'm probably missing a few. They all have pros and cons.
For a Surly LHT I'd probably just do DT shifters.