Defining an acronym when using the plural of the term? [duplicate]

Possible Duplicate:
What is the correct way to pluralize an acronym?

I am defining an acronym which will be substituted for some unwieldy term in a document.

One thing Gary has talked extensively about is his inclination towards extracting domain objects into Plain Ruby Objects (PRO).

The trouble is that the first time I use the unwieldy term (Plain Ruby Object), it is plural. However, the acronym is more useful in the singular.

Should I just hold off defining the acronym until I use its singular form further down the page?

Either recast the first use of the full expansion into the singular, or else write the acronym in the plural.

• One thing Gary has talked extensively about is his inclination to extract a domain object into a Plain Ruby Object (PRO).
• One thing Gary has talked extensively about is his inclination to extract domain objects into Plain Ruby Objects (PROs).