If this is a requirement for you, you might consider posting a feature request on the forum:
Feature Requests for cPanel/WHM
Otherwise, if you are unable to develop the component to function, you might hire someone to try to get that type of ability setup before any such feature is implemented:
Dev & Sys Admin Services « Application Catalog
A note for the feature request, I highly suggest being very specific that you require the following:
I would like to request that cPanel database users are able to log in with the database username and password to PhpMyAdmin rather than restricting login to the main cPanel username and password for PhpMyAdmin. This will allow individual database users to manage their database independently, similar to allowing email users individual email account login for webmail. We already allow remote connections to individual MySQL databases to manage the database via the cPanel database username and password.
If you phrase it like that, you might be able to propose a worthwhile reason for the feature to be considered.