1) I don't think that such dependency is really an "attribute" of a class (in terms of UML). I would show it as an "aggregation".
2) The purpose of any UML diagram is not show "everything you can show". The purpose is to inform the reader about your architectural decision, at some certain level of abstraction. If all your dependencies belong to the same level of abstraction and you can't place them all into an easy-to-read UML diagram - it's a sign of poor design. Re-design your architecture for better cohesion and less coupling.