Best practice for a one prim multi vendor interface

Hi;

I am currently building a multi vendor. But i need this vendor to be a single prim.

Currently the vendor has got these functions:

- give away a notecard for free
- give away a demo object for free
- sell 1 or more items of different price.

I want to make the vendor clickable in some way. So i think of using the new
functionality in LSL:

llDetectedTouchST and llDetectedTouchUV

The idea is to make a texture with "buttons" on it. Then examine where on the texture
the user has clicked and then react accordingly.

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The other idea is to rez temp-objects when the vendor is clicked. Each temp object is a clickable "button" appearing on the surface of the vendor. Clicking on the button gives away or sells its content on touch.

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Do you have any advice, what would be the best way to go ?
Is the llDetectedTouch functionality reliable ?
What caveats are to be taken care of with temp rez objects ?
Do they add to the prim count as long as they live ?
Is there any other possible way to go, which i have overlooked ?

thank you for any hint.