I have the fx1 and had this same question. The answer for my camera is no, there is nothing within the camera that will downconvert and simply crop the edges. However, it is relatively straightforward to capture the widescreen HDV and then convert to 4:3 SD in Vegas, and this also gives you the incredibly useful advantage of being able to pan/crop the widescreen so that if you mis-frame the original shoot, you can frame it perfectly in post. Also, you can create some fairly significant zooms in post because you have a LOT of resolution to play with (1440x1080 vs. 720x480). Basically, you can do almost a 2x zoom before you start degrading the resolution to less than SD.

Remember to choose Best when doing the Render as when rendering HDV to SD.

Here is a link to a long description I gave two years ago about my HDV to SD techniques:

My workflow for HDV to SD projects

Here's a permanent link to the mask file:

Mask

and here's a download link to the same file, good for seven days:

Mask Download