You should be able to manually enter them, one at a time ... but you'd have to have them in the correct format or your waypoints could show up as being somewhere in Siberia
I've used this site to translate/convert GPS coords off a website that our F&W puts out : GPS Coordinate Converter, Maps and Info
It's been so long since I did this that I'm not sure which format the F&W site used, but only the "Decimal Degrees" and "Degrees Minutes Seconds" or "GPS" formats need be used ... you can totally ignore the "UTM" format.
When you enter the coords, you should see a waypoint appear on the map on that site ... indicating where those coords are. Then try using each one of those 3 formats in your Hook & see where the waypoint shows up until you figure out the right one.
I "believe" my E5DSI unit used the "DMS" format, so I'd try that first. When my E5DSI died I replaced it with a Hook 7 and manually entered all the coords that I had written down & entered into the E5DSI unit ... and the Hook unit accepted them and shows them in the correct places.