Not that I'm aware of. At least not as supplied by Captivate.
I use a Microsoft Mouse that came with Intellipoint software.
The software allows me to click a special button that provides a
zoom in. As I'm able to screen capture the zoomed area using
SnagIt, maybe Captivate would do the same.
If you have a similar setup, perhaps you could accomplish it
In case you wish to try, the Intellipoint software download
is listed at the link below.