The same you can do with Import button. You can see this button at the top right side of the JBoss Tools Palette.
By clicking on the Import button you will see the Import Tag window a similar like in the Drag-and-Drop method. On this Import Tag form you can select Browse... to locate the tag library that you want to add. Also you need to set the Group name to which you'd like to add your tag library. And like in the previous method you can add it to an existing Group or create a new one.
Now select the TLD file you want to be added: