Yes, it should work, and making a fake DLC is the only method I know to play multiplayer modded Civ5 games!

cheers

Do I have to just copy the mod to the Expansion2 folder and thats it?
There are no XML-Files in the SmartAI folder like in the multiplayer modding example.
Just the .dll file. Do I have to make an entry for the DLL file like for the XML files in the example or is this not necessary?

EDIT: Or do I have to replace the .dll file in the Expansion2 folder with the one that comes with smartAI?

@RoseFlunder - I linked the wrong guide above! Subscribe to this, and follow the instructions of this:
http://steamcommunity.com/sharedfiles/filedetails/?id=361391109

In super simple steps:
1. Start the game up regularly, Mods > select all the mods you want in your modpack, including the one I linked > Start a single player game
2. Disable anti-virus (it's safe, just the process reduces from about 2 hours to 2 minutes)
3. Minimize the game, go to Steam > Tools > Civ 5 SDK > Firetuner
4. Expand the top left dropdown menu, select the first option, which is a directory (ex. C:/blabla)
5. Also in Firetuner, in the command text field, type CreateMP() and hit enter. Wait till modpack is compiled, you will see "All done!" in the console. (if you haven't disabled your anti-virus, this will take about 2+ hours)
6. Open the game back up, close it. Close Firetuner. Enable anti-virus.
7. Navigate to <civ 5 installation dir>/Assets/DLC. You will see a new folder called MP_MODPACK. This folder contains all the mods you've selected in step #1. To play with friends, just give them this folder (through any file-sharing website or USB), and make sure they have it in the same directory.

Note: Known issue I've encountered, you can't use EUI (enhanced user interface) with a modpack, so it's one or the other. If you are using EUI, before following the steps above, take it out of the Assets/DLC directory, as the guide I explained will try to include it in the modpack, and corrupt the UI.

If you need a hand with this, feel free to add me on steam.

Cheers!

Thank you for your answer. I made everything as you described. I now have the MP_MODSPACK folder ready. Is there some way to check if it is really activated when i start a new multiplayer game? There is this section "allowed DLCs" where gods & kings, bnw for example is listed, but MP_MODSPACK or sth. is not shown there. Is it active nevertheless?

Yes - as long as the folder is in the Assets/DLC directory, it'll be active.
Remember that you would just start a new multiplayer game with as you regularly would, no need to activate it. That's the beauty of using this method, once it's placed in the directory, everything else is taken care of.

Did it work? Did you experience desyncs?

It was a while back and I don't quite remember. If a mod isn't compatible, at most you will experience glitches like buttons/UI not behaving correctly, but not desyncs.

I do remember trying this one out in multiplayer however, and was pretty fun:
https://steamcommunity.com/sharedfiles/filedetails/?id=312060464

I would try them separately (obviously). If you end up trying both, do let me know which one you prefer!