Sorry, but no. You will need the base weapon to obtain the associated WS. There's little-to-no supposing about it. SE have all but outright explicitly stated this in an official announcement.
http://www.playonline.com/pcd/topics...20/detail.html
Note the line which is written in bright, look-at-me-I'm-important red:

F-WORD
The difference between your example of a Dynamis item and this Nyzul item is simply a matter of time and convenience. Dynamis is an event involving a large group of people with rigid time-openings that takes several hours. Nyzul is something you can take 5 mediocre-geared 75s into for an hour or two whenever you feel like. This is what seperates Nyzul from most other endgame activities (and what makes it, according to SE, accessible to 'all players'). It may even take a few years to make your progress all the way up to your Mythic Weapon, but a casual player can do this without being tied to rigid, large-member group events.
/snigger.. Rigid large members.
