As a dissertation advisor, how can I best help a "typical" graduate student?
Let him teach. 

Assuming that he decides to make plans for working at a LAC or a branch campus of a state university he will need to be ready to teach the day he starts. So encourage him to take that part of his professional training seriously. 

If your soon-to-be student is really going to end up in a small department a very helpful thing is that he can continue his research more or less independently. There is the internet but it is not the same as having half a dozen people working on the same topic just outside your door. This, I feel, is more important to his future than whether or not the topic he decides on has a large or small buy in cost. That being said he will want to have some facet of his research program that can be explained to a general mathematical audience, but this does not have to be all of it. 

If all else fails, find a friend of yours or a not-so-recent graduate who teaches at a school like this and ask them what they want to see in a candidate. That should give you a good guide for what outcomes you should work for in your student.