Assuming your submittal tasks have an effect on your programme, there is a way to partialy get around this, as I had asimilar problem. As julie says, use milestones to mark each submittal, but use a start and finish milestone with a lag- if task Submittal X has a duration of 10 days, predecessors A and B, and successors C and D, then set up tasks as below

Submittal X- Start Pred A, B, Successors Submittal X- finish, with lag of 10 (duration of task)

Submittal X-Finish Pred Submittal X-start, succ C,D

both as milestones. this will allow you to preserve the shape and integrity of your programme without giving any % complete.
This will effectively give you a task of any length with 0 duration.