Hm. well if it's just to preview a journal entry, a whole browser-type interface isn't necessary at all. maybe just either a pop-up window or a replacement of the current text box with the gtkhtml mockup of it.. nothing fancy, no need to see the whole livejournal friends page.
The idea is for the interface be user configurable. For instance, the interface could look exactly the same as the original logjam interface. Or you could add a view for your uncle bob who just posts to his html website. Or a view to look at your own journal. Or add an advogato journal entry tab.
Here is an example of the xml file that produced the above screenshots:
Do you have a snapshot available for download? I want to figure out how integration into Evolution works, and I'm running a binary RPM release that I can't afford to download the source for (dialup link).