If you don't want to use the kobopatch system and because it's an English dictionary, you might want to try the following simple trick:
- Rename the dictionary from whatever.zip to dicthtml-en-en.zip
- Copy it to the same .kobo/dict directory you used previously
- Reboot
It should now appear in the dictionary drop-down menu as 'English - English' right underneath the Kobo default 'English' option.