I would enter their file names under textures and tell which sub-objects use which one.
Can't do that in PCS2.
You have to make sure they're assigned already, in some way that will export from blender (no idea how, ask an actual blender user).
What I meant is that if the texture names end up being something like 1_Gilga and 2_Gilga (due to a hypothetical 8-character truncation and auto-number of some sort), as long as in PCS2 you see the pink marks over the correct polies, it doesn't matter, simply rename, but you have to ensure that you have at least 8some* texture assigned to the polies already which you can see the pink lines in PCS2 when selecting the texture name, otherwise it no work.
I mentioned this because I just assign dummytextures from a set that I know exports correctly, then put the correct name afterwards in PCS2, since the 3d studio max exporter likes adding the 1_ and 2_ before the textures anyway and doesn't like certain texture names (for example, it hates the names 3DS max autogens for AO bakes for whatever reason and refuses to export it with that texture assigned, but this is getting to be an aside). HOWEVER, this
probably is not relevant to you, since the Blender DAE exporter presumably behaves differently.