Perhaps the most important question is: why do you want to?
There are a lot of groups out there that they that "Agile Development Practices" will make a traditional project complete faster. While this isn't strictly wrong, it commonly fails - the main reason for this being that without a proper understanding of why different practices work, its hard to pick out the ones that will help and ones that will just trip you up if you try to use them in waterfall.
In the interest of answering the question, I'd say you should look into Lean and Kanban. These are pretty compatible with small-batch waterfall projects, but it's fairly likely that they will require significant changes at the management level. You can also look at some of the technical practices you see in XP. Pairing and TDD can chop out some of the waste that naturally arises in software development. Of course, the challenge with these is also that people who are driving dev teams in the manner consistent with strict timelines frequently view these approaches as "inefficient" and fight against them.
Now, if you want to implement a framework like Scrum because the organization really wants to make that switch, then they need to drop the umbrella waterfall structure. Like any other change management, there are broadly two approaches to this. You can change rapidly and remove all of that structure at once. This has the advantage of getting the pain over and done with. Or, you can take small steps - creating small, protected pilots that are not subject to the timelines. Realistically, unless you have some really strong change agents and leadership behind this, consulting with someone who helps organizations through these transitions would probably be very helpful.
