I had a similar problem on a website I built full of case reports. I wanted the case reports where the victim name is known to sort to the top, because they are more compelling. Conversely I wanted all the John Doe cases to be at the bottom. Since this also involved people's names, I had the firstname/lastname sorting problem as well. I didn't want to split it into two name fields because some cases aren't people at all.
My solution:
I have a "Name" field which is what is displayed. I also have a "NameSorted" field that is used in all queries but is never displayed. My input UI takes care of converting "LAST, FIRST" entered into the sorting field into the display version automatically.
Finally, to "rig" the sorting I simply put appropriate characters at the beginning of the sort field. Since I want stuff to come out at the end, I put "zzz" at the beginning. To sort at the top you could put "!" at the beginning. Again your editing UI can take care of this for you.
Yes, I admit its a bit cheezy, but it works. One advantage for me is I have to do more complex queries with joins in different places to generate pages versus RSS etc, and I don't have to keep remembering a complex expression to get the sorting right, its always just sort by the "NameSorted" field.
Click my profile to see the resulting website.