Speeding up the Query Parameters Dialog in the SSRS Query Designer

Boyan Penev recently blogged about the virtues of setting default parameters and he's right: it's a good idea to set parameter defaults. However I was with a customer yesterday who were waiting for a really long time to even open the Query Parameters dialog in the SSRS query designer. I was a bit curious as to why this was, so I ran a Profiler trace. What I found was then when I opened the dialog when there was a default selection made, for example: