I used to get so annoyed by this I'd deselect Bloodmoon from my load list just so I wouldn't see the rumour remark.
Then finally I thought I'm not putting up with this anymore and hence this tiny mod which filters the reference to Solsteim in the latest rumours topic.
Now the only person who has had their son sent to Solsteim is Jonus Maximus the Knight wearing the full Imperial Templar set of armour at Ebonheart. Other than Jonus only NPC's who are the Agent class and S'virr the shipmaster to Solsteim will introduce the topic Solsteim. I figured agents would know this type of rumour.
Once you have spoken to an agent or Jonus or S'virr about Solsteim then all the folks in Khuul (where you catch the boat to Solsteim) will now be able to tell you about going to the docks to find S'virr as per ususal - I haven't touched their filters at all.
Download at PES - http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=8471