I think it is important to stress the fact that the funding agency, as irksome and bureaucratic as it may be,
>>> gave you free money. <<<
(edit: see explanation below of what I mean by this)
Let me say it again: an organization gave you money that was theirs and that they didn't have to give you. Maybe they were annoying. Maybe they didn't give you as much money as you hoped they would. Maybe they imposed rules and restrictions that you disagreed with or that seemed unreasonable to you. The fact remains, they willingly and voluntarily parted with their money and let you spend some of it. All they are asking for in return is that you give them an acknowledgement. Is that really so hard? Just write the acknowledgement they are asking for, in the precise language they specified, not a word less or more. Honestly, writing anything else sounds extremely childish and unprofessional to me
Edit: some people seem to be reacting negatively to my use of the term "free money", so let me clarify what I meant. The point is that this money that was given to OP by a funding agency comes with much fewer strings attached than money typically exchanged between two parties as part of a normal economic transaction. With grants, there are usually no specific deliverables, nor a strict schedule for the creation of a specific product or output of the research. There are some well-defined restrictions on what the money can be used for, and an expectation of an annual report and of a minimal amount of recognition on the part of the recipient in the form of an acknowledgement, and that's basically it.
We in academia are used to these sorts of arrangements and don't think there's anything unusual about them, but it's important to remember that to people outside academia, who can only dream of being given any amount of money (let alone many thousands of dollars) by anyone under such loose terms, this can appear downright amazing, and is perceived, to a very good degree of approximation, as "free money".
Finally, I googled to see if there's a technical definition of the term "free money". There doesn't seem to be a completely standard definition, but at least Businessdictionary.com defines it as
Drawbacks, grants, subsidies, tax-breaks, and other such means employed to keep some firms afloat in order to (1) save jobs in depressed areas, (2) protect certain industries such as agriculture or defense, and/or (3) promote research and development.
so I think my usage is within the accepted meaning number (3), if one makes allowance for the academic context of the current discussion.