This works great from konsole, however I have added:
dcop kdesktop KDesktopIface popupExecuteCommand
to my kbfx menu and it does work
but on my task bar I get two 'Run Command' instances - only one gui dialogue box, though.
The second instance has the turning egg timer in the task bar for 30 secs then disappears.
Even if I start the run command then immediatley close it (via clicking cancel) the second instance in the task bar still shows as 'Loading application' for 30 seconds.
I am very happy with your solution and it works great

Curiously, what would cause the second instance to show in the task bar?
Double checked and the command in kbfx menu is just:
dcop kdesktop KDesktopIface popupExecuteCommand
but only does the above when launched from my menu not konsole, hmmm?