Usually both the context menu key (to the left of the right Ctrl key) and the combination Shift+F10 bring up the context menu.
However, if the application is relying on the mouse pointer's location when opening the context menu to provide additional entries (such as the spell-checking stuff), then you can't do much. IE7Pro's spell checker does that too and it annoys me. Word gets this right (but for Word it's a core feature, not something tacked on which looks nice on a feature list).
Actually, I'd consider that a bug in the respective application as the context for the context menu is not the mouse pointer when opening the menu by keyboard. Especially not if it's inside a text input field.
But short of reporting a bug to the Chrome developers there probably isn't much you can do. Maybe you could whip up some ugly Autohotkey evilness which moves the mouse pointer to the location of the text cursor when pressing the context menu key. But since browsers don't use native controls but instead render everything on their own you probably can't do much from there either (as it may well be impossible to figure out where the text cursor is located).