That's the sort of thing I had in mind. Large quantities of tape or elastic bands securing the bag onto a small hose, and you've got the connection to the measuring chamber. The nice thing about this approach is it's all low tech and doesn't need much construction. Not as refined as motors driving nuts spinning around threaded bars all mounted in an assembly driving a syringe and all that, but I much prefer to get something simple working and then improve on it as necessary.