We have a big project broken up by concerns, each concern has it's own VS2010 solution - all good.
For the purposes of having just one top level solution to open so an entire system rebuild can be done, I'd like a top level solution that includes the lower level solutions.
It doesn't seem to be possible - all I can do is add projects from the lower level solutions meaning I pretty much have to do that twice.
Is there a better way to manage this, and if so, what?
No, there's no hierarchy for solutions. The only option is to add the individual projects into one solution.
It sounds to me like you have way too many projects. The only level of hierarchy you should need is a solution grouping together multiple projects. Use folders to hierarchize within projects.
Beyond that, you shouldn't have to even open up Visual Studio to create a build, so there's really no need for a solution at all. Investigate writing and using a build script to automate this.