Wow, so many replies! Thanks at everybody!
The weighing method (which I couldn't find with the search because it never even crossed my mind to browst the clips for the topic ) seems like a pretty good approach which I will definately try, paired with the toothpick idea if only small dots are required.
Did anybody try a syrenge for small amounts of colored lines? I thought it might work, but am not really sure. The icing would really have to be fluid, though... hmmm.