An alternative to basic putty? -Updated

In the process of writing a sanding tutorial, I ran into the problem of trying to explain how to use basic putty to fill any holes, gaps and sink mark on a model kit. If I were to use putty to fill, then I have to paint the model kit, since basic putty only comes in white and grey. How are people who do not intend to paint going to fill the hole? I am now trying out the alternative means to putty and people who do not intend to paint can also use. Here is the jist of the idea.

1. Cut off the runner of the same colour as the plastic part I intend to fill.
2. File it into fine powder.
3. Apply a thin layer of extra thin cement over the hole.
4. Sprinkle the plastic powder over the cement.
5. Compact with a paint stirrer.
6. Apply another thin layer of extra thin cement over the plastic powder to dissolve it.
7. Repeat the process until the hole, gap or sink mark is filled.
8. Wait for 1 to 2 days for the plastic to harden before sanding.

I think the theory is sound, but not sure if the above method will work in practice, but I will give it a try. Will update on this issue. Any other suggestions or comments for this problem are welcome.

Update
I tried the above method and the results are as follows:
1. It works for the softer plastics (probably polystyrene).
2. The results on the harder and more brittle plastics (probably ABS or similar plastics) is not as good, because the cement cannot melt the plastics effectively.
3. Another problem is the mess leave behind if not done properly. (I destroyed my old coffee bean grinder, trying to grind the plastic to powder form. Lol, I got lazy to file)

Unfortunate for those who do not wish to paint their kits, but I am left to conclude that using putty may still be the best option yet.

As many modeller knows basic putty has it's own problem to be discussed at a later time.