Here is a workflow I came up with using the subclipping function (CMD+U).
You might want to make a copy of your timeline and place it in a new bin. That way the subclips will land in that bin, making them easier to locate later.
Find your first frame to export and Mark in and Out. Go to Modify > Make Subclilp (CMD+U). This will create a subclip with a single frame duration. Repeat for each still frame to export.
Select all of the subclips (but not the original sequence) and go to File > Batch Export. Now use the setting function to select the type of file, and the destination folder. Be sure to check Use Item In/Out. JPEG didn’t seem to work, but PNG did. You can use an image editor to batch convert to the format of choice.
The downside of this is that the exported file name will be something like Sequence Name Subclip 1, Sequence Name Subclip 2, etc. You can use batch renaming software to rename the images. Instead of subclips you could use the marker function and set the durration to 1 frame.
I hope this helps.
Lee Berger
http://www.leebergermedia.com