Perhaps there could be a simpler solution;
The Torture carrying the fleet commander can upgrade its hits to 8 and then purchase an additional weapons system. Probably the cost for this would be somewhat steep, maybe 35? points.
Great idea! An upgrade option is best fluffwise solution. Simple and also will not cause 'new ship' trouble!
How about this;
If fleet is worth over 750 points you can upgrade Dread Archon's Flagship for 35 pts.
Upgraded Dread Archon's Tortune Class Cruiser will have 8 hits and may choose one additional weapon from Tortune Class Cruiser ship's weapon options for given points.
For fluffwise name of this upgrade will be a special character like Duke Sliscus's Flagship
By the way i just read 2010 FAQ and it seems this is not comfirmed
;
Dark Eldar:
Mimic engines for free
Torture can buy two impalers for 20 points, not 2 for 20 each.