No, there currently is no way to do that with Workbench. The problem with writing something to do that is that it has to operate over multiple Keygroups at once, and the distributed agent based architecture of EigenD makes that kind of thing really difficult to implement as Keygroups are all seperate agents, at least in a non-bodgy, non-ugly way. There is a desire, not terribly difficult to write, to be able to graphically edit each Keygroup mapping but this is harder than you think too as EigenD is currently 'instrument agnostic, in that it doesn't care about the actual shape or layout of your instrument and doesn't know about it either. Given the prevalence in new instruments being used with EigenD this is likey a feature that will be retained.
Remember there is also 'choose mode' in the Keygroups, which allows you to press the keys in turn to set up a mapping, which can make things a lot faster if you're building a big new setup.
The reality of this is also that it's not actually something you'll do many times, so expending a lot of development effort to make it easier is slightly wasted. So much of musical learning is practising to embed muscle memory, and you'll find that once you have a Keygroup layout you like you'll 'practice it in' and never really want to change it. It's a task that happend once in a blue moon after that, and a little inconvenience is not so bad, there are certainly a lot of more common and frequent tasks that probably cry out for development more. Having said that, if you can code a bit by all means have a look at a graphical Keygroup editor, it would a nice addition and I'm sure appreciated by all...
John