I tried this and it seemed real handy, at first, on the small pieces, but when it came to cleaning up the seams and ejector pin marks your back to a clean piece of plastic.
So now I take the pieces off and clean them up one by one, then put the model together in sections, that way I only primer once.
Never building to where I can't paint, it takes a lot longer, but I got plenty of time.
This method might not work for all, but works pretty good for me.

I find that many small parts, such as tools, can be cleaned up on the sprue except for the attachment point. This leaves just a small dot of paint needed before attaching to the model. The other method I use is to remove small items from the sprue and stick them to a piece of wood with double-sided tape, they are painted on the tape and then just switched from there to the model.

Thank you Dave for getting me to think again, before there was a lot of parts that I couldn't clean so I gave up on trying to clean them on the tree, but the tow hooks are so fragile anyway that on the tree is that third hand I needed, cause they are so small, and so hard to hold, the tree makes perfect sense.
After I read about you on cleaning tools I tried these hooks and it worked perfect. I believe in giving credit where credit is do. Even though you didn't mention tow hooks you did mention small items, then it got me to thinking, but still it doesn't fix it for all, it did fix the problem for the hooks, and hitches.

Best Regards Kerry

actually i would actually attach everything to the model, paint the model,then paint the small parts such as accessories etc, what do you think?

I was talking about the priming, but the final painting, it depends on what it is, and how hard it is going to be to get to it for final painting, somethings I haft to paint before I put them on, cause there will be no way to reach with a brush afterwards.
I've done that before, and to get the thing painted the color I wanted, the surounding items got hit to, so I had to wait until that dried and repaint them again,back to their original color,so now I watch that.
I love to work on a model, but when it comes to correcting mistakes then some of the fun is removed.

I am in awe of the modelers who glue all the tools and stowage to the vehicles and then paint the whole thing and then go back and paint the tools.

I find that removing the tools from the sprue, clean them up, paint them, then attach them to the model works best for me.

I tried, early on, to paint the tools on the sprues, but ran into the problem of cleaning up the mold seams too.