What is maddenly irksome is that the currently assigned keywords appear almost within reach in the filter panel ... but alas, it is not possible to use that panel to assign those keywords to new photos.
You can export your current keyword list as back up and create or import a temporarily dedicated shorter keyword list.
But if you look at the metadata panel IPTC Core there is also the option to show the keywords applied to the image (if they don't show use the setting in Bridge Preferences Metadata Tab to select it to show)
Drag and drop is not possible but copy past is an option. Using collections you can select the files you want to apply the same keywords to, and when your search result is complete select the file that has all the correct keywords, copy the complete line of keywords, select all and paste the info in the same line to apply al keywords in one go to all selected files.
Is that about what you are looking for or am I completely misunderstanding your wish?