Insertion of jsp fragments from palette is managed by org.jboss.tools.jst.jsp.jspeditor.dnd.JSPPaletteInsertHelper class.
On insertion it defines a namespace for inserted tag in the root document element. Namespace and prefix are received from palette.

Sometimes it is required to define a several namespaces for one fragment from palette. For example, fragment is some jsp tag, containing a "<jsp:attribute>" child element, so "jsp" namespace should be defined in concert with those tag namespace.

Potentially i can implement this functionality myself and submit you a patch, but i'd prefer to do it in accordance with DND code owner's considerations.