Biometric devices work by reading the ridges in your fingers. If the ridges are not well defined, they can not be scanned.

One way is to encourage employees to drink more water. After that, you can try third party tools like these:

http://www.crimescene.com/store/index.php?main_page=product_info&products_id=297

http://store.sirchie.com/EZ-SCAN-Ridge-Enhancer-15-oz-P2345C441.aspx

(Note, links to these tools were sent to us by digitalpersona and not tested by our team as of the date we posted this entry)