Parenthetical pluralization of words ending in '-y'

Sentences constructed with a word written in the singular and parenthetically in the plural are straightforward when that word does not end in -y, e.g.:

List all applicable employee(s).

How does one handle words ending in -y? Is this correct:

I will attend the party(ies).

An alternative to the use of parentheses to provide both singular and plural forms is to separate them with a slash:

party/parties

This would be preferred in this and other similarly awkward formations such as wife/wives, and in special cases such as mouse/mice.

"Party(ies)" is certainly used in official contexts.

https://www.google.com.au/search?q=%22party%28ies%29%22+site:.gov

I think the following may also be an acceptable way of dealing with an uncertain plural ending in "y":

part(y/ies)

A safe, formal alternative is of course to use the singular and the plural with or, e.g.

I will attend the party or parties.