I managed to solve the issue this morning after reviewing the source to the mime tools plugin.
The following lines of code resulted in the data being displayed correctly.
SendMessageW(nppData._scintillaMainHandle, SCI_TARGETFROMSELECTION, 0, 0);
SendMessageW(nppData._scintillaMainHandle, SCI_REPLACETARGET, len, (LPARAM)text);
Thank you for the assistance.