Getting back to the orignal question...
Your Scaven Thrower is 7337 Pass, Sure Hands, Dump-Off, Accurate. (Right?)
So on a double roll take NOS... no question about it... now he doesnt even need a cage arround him... just a Gutter Runner within Quick Pass Range that is supported so when they Blitz him he only has to make a 2+ Pass with his Pass Skill Re-Roll.
AFAIK Dump-Off if thrown accurately and caught counts as a Pass Completion and you get the SPP for it. So after Dumping-Off alot you'll get your next skill which will be 'Safe Throw'. After that the players development is complete for his purpose. (Which is a good thing too, cause he'll need 76SPP total (or 25SPP more from his 51SPP) to level again. Hopefully he doesnt age
In an Elf Team Id make one of the Throwers essentially the same, but there isnt any need to get Accurate, since you throw Quick Passes on a 2+ with Pass Re-Roll anyway. So for his 4th Skill you'd get Sure Hands to save on Re-Rolls.
---Korhil