The plaits might be fiddly given the head.
There used to be some daemonette heads with long tongues? Or were they Dark Eldar somethings? There are
GSC heads with ridiculous tongues. Might be able to convert or snip and glue.
The tongue shouldn't be. Remember, a tiny drop of super glue at the mouth will adhere
GS instantly. If you don't feel you can sculpt the
GS normally for this, here is a technique that might work.
Tip #1: take a teeny bit of
GS roughly the tongue size you want (I'd roll out a flat wedge, thick but short) and roll the end that will be the tip of your tongue in a toothpick so it acts as a handle. Super glue the base to the model's mouth, then use the toothpick to stretch/shape your tongue to length and bend. Let it harden, cut the toothpick free.
Tip #2: Fingerprints on the
GS will look like the normal texture of a tongue.
I am not saying this is easy at the scale you would be doing his tongue, but it is doable.
I used this technique for some tentacles, as well as guidon banners for my rough riders. This won't be great help since its a guidon, but just to show a result: