I think you can get rubber covers for bar ends. you could also buy the padding gel and foam handlebar tape that people use for taping up road bars.
Flat bars are actually kinda brutal in terms of hand positions - so something you might want to consider is getting butterfly or trekking handlebars, they give you a lot more positions. they get taped up with handlebar tape.
If you want to stay with straight handlebars - consider getting some ergon grips. They're currently on sale at REI & at performance bicycle.
Other handlebars that you could consider are the soma sparrows, but I don't know how they do for long tours.