rules - Can possessives in the middle of a word exist?

According to one online dictionary, the apostrophe-s combination is

an ending used in writing to represent the possessive morpheme after most singular nouns, some plural nouns, especially those not ending in a letter or combination of letters representing an s or z sound,

Note the opening, "an ending". Does this mean that an apostrophe COULD NOT be a possessive elsewhere? I have been reading up on the words "bridesmaid" and "groomsman" and according to that same source, the s in the middle is a possessive. (Other sources make the s an "unetymological [which] began to appear by 1794")

I'm asking a theoretical question -- could the word be written "bride'smaid" (and/or "groom'sman") or is there a hard and fast rule that possessives are only indicated at the end of a word? (I have yet to find other words besides bridesmaid(s) and groomsma(e)n to which this would apply)