Unless I am missing some keyboard shortcuts somewhere which google failed to enlighten me about.

Which is entirely possible. But I am kind of annoyed by this particular software feature.

there's a link under the box where you'd ordinarily type

it says "private plurks, languages, and options"

if you tab past the button to enter your plurk, it's the next thing the tab hits

so, once you log in: hit tab once, it takes you to the menu of dumb action words (feels, is, shares, etc)

hit tab a second time, it takes you to the box where you would type a plurk message

hit tab a third time, it takes you to the box where you would press enter to send the plurk

hit tab a fourth time, it takes you to the link of "private plurks, languages & options"

hit, say, the spacebar when you are on that link, and it opens up the option to mark a plurk private

"who can see this plurk?" and 2 radio buttons.

the 1st is "the whole world" and is selected by default

the 2nd is "only my friends"

I got all that, but I couldn't figure out how to, say, send a plurk to, like, two of my friends.

You're supposed to be able to select "only my friends" and then have a box wherein you can type the names of the ones you want it to go to