So I gave up on that.
But what am I trying to achieve?
I have several brokers on the same PC so that only requires one shared folder on the same disk,
but I also have several brokers on other PCs linked by a network.
So what will allow me to have a master on one PC and slaves both on the same PC and on other PCs?
Part of the answer is bitTorrent-sync which I already use to share data over the network. Not everybody likes their approach to security. Many people are using an alternative called syncthing:
https://github.com/syncthing/syncthing/releases. I am sure there are others as well.
The other part is to have the same shared folder on each PC
e.g. c:\Users\Public\mt4trades\
I found some examples of reading and writing orders to CSV and example of generic file operations outside the Empty4 folders.
This is the link to a file which wraps Windows file operations. There are a couple of issues that the compiler complained about but after a couple of tweaks it compiles even though the source is from 2009.
https://dl.dropboxusercontent.com/u/543 ... inFile.mqh
Update: This method of calling WINAPI file operations nolonger seems to work.
There is an example of reading and writing orders here but it is quite out of date now and is limited to Empty4 sandbox folders:
http://code.google.com/p/Empty4-trade-copy/
but if we combine these two sources it might be possible to get a basic trade copier working without too much work.
Update: This does the basic job of updating a CSV file in response to a change in the orders.
It now looks like it won't be possible to use a common shared folder on each harddisk. The next task is to see if the sync-app can sync files from mt4Terminal_1\MQL\Files to the same folder of several slaves.
To be continued...