It's and Art more than a Science
We apply agile techniques to infrastructure projects within our organization as a means to accomplish a great deal of work that must also be done right the first time. It's the only way to eliminate a backlog of technical debt.
The thing that is different about using Agile within Infrastructure is where you focus your agility within the process of implementation.
To be fair.. we actually blend 'waterfall' with 'agile'... and with it we are capable of getting projects started sooner, and completed faster simply by using an agile approach to the 'planning, design, and testing' phases so that 'implementation' goes off without a hitch, and 'maintenance' (or residual effort) is kept to a minimum. Does that mean we Scrum, use swim-lanes and sticky notes, and hold daily stand-ups... no. But we could... if the scale of the project warranted it.
The biggest complaint about 'waterfall' is the analysis-paralysis trap that can occur in the planning phase.
We approach elements of the 'planning, design, and testing' as 'stories'.
We iterate on the stories till we have a 'good enough, let's get started' understanding and all involved can be 'leveled'.
Along the way, some of these items can get polished and perfected, if needed.
Craft-fully applying an agile mind-set to the planning is the trick. Break the planning phase down into 'individual stories'. Focus on 'chunks' of the planning at a time. Iterate on those chunks to the point that they offer enough value to 'the project'; and then move on to the next chunk or parse out different chunks to separate 'teams'.
The design and testing phase can be done in a similar fashion. With the objective that the 'implementation' is executed timely, includes safe fall-backs, and the regiment for execution be well choreographed; use an iterative approach to produce the 'things' you need for implementation day.
Where is the low hanging fruit, and where is the tough meat? Knock out the easy, while iterating on the hard.
Is there a bit of 80% (planning) / 20% (execution).. yeah.. so apply Agile to the 80%.
So what is the trick...? Clear, obtainable goals and objectives... what are the problem(s) to be solved? This is what the Product Owner/Manager does in Software Development. For Infrastructure, this is the value the organization, department, or a given project.