if they ever get around to fixing rtt it might be possible to sctipt stuff like this in

come to think of it you could probibly do this with an animated texture, well sorta. you have several versions of a texture, one with full alpha, and several others incrimentally less alpha. then you tell your script to swap out the ship textures for progressively more transparent ones untill youre using very little alpha. then switch over to invisible when fully cloaked. if i did it id have a few maps with a noisy alpha map in the 0-8 range on the grey meter. then you randomly swap between them. this should cause a ghostly shimmer to hint you that the ship is there. or do like they had in avp, where you get the shimmer texture while moving around and go completely invisible when youre hardly moving.
side effect is you have to have this done for every texture the ship uses, thus increasing texture usage. could probibly be maid faster if you could replace say a -trans map for a model, without touching the diffuse texture. you may also have problem replacing ships that already use animated textures, like thruster flames. least in my build i found i had trouble indexing textures on ships with animated parts. should probibly mantis that bug if it hasnt been already.