If the quest allows the lower levels, but has a gap level, you request it at higher level, do most of it, then shroud down to an appropriate level. Usually you have to drop to just 1 person in the task to do this, then quickly re-invite others that have shrouded down and lower levels you want.
Most DoDh missions have a minimum level of 65-70 to do them though. Not all, but I believe the one you listed is one of those. So you could try a lower shroud if need be to get within the 15 level range. Also, it's an instance, so you will want someone pre-shrouded or ready to zone in as soon as the 1 person shrouds downs and re-invites to keep the instance up, if the loot has already dropped (And if it it's a final chest loot, just leaving with make it go poof, so won't work, as you would have to have shrouded ealier than that).
Hopefully that clears enough. It's early, and re-reading it sounds pretty garbled for someone that wouldn't know what I'm talking about already.
Basically it comes down to a couple of things. Can't leave an instance once the chest pops. Can't usually invite people once the chest pops. If the instance allows the lower levels, most of the time, all you need to do is shroud down to a level within 15 of the lowest person. Some (many) instances (tasks) have a minimum level requirement.
If it's not an instance and the task doesn't have a minimum level requirement, the shrouding should always work, unless it's the final quest reward, then you'll have to be able to do the last step shrouded. When it's just a hail, that is perfect for these types of situations. Also, non-instanced ones, can alot of times be done only by the lower levels in the task, if they can get it, and then the higher levels helping out with the work of the task. This is quicker and easier than shrouding. Some tasks will have a minimum request level, but not taskadd level, and that's where shrouding is really helpful. Request the task at the level needed, shroud down, invite the others, do the task,
There's many options.
Yther Ore.
Edited, Sep 2nd 2013 4:21am by Yther
Edited, Sep 2nd 2013 4:26am by Yther