Launch FileMaker on A client machine.
Instead of opening a file, create a new database.
No need to define any fields or tables in this file.
Write a script with this line in it by selecting Manage Scripts and clicking the New Button:
Select this script step and add it to your scritp:
Open File 
When selecting the file to open, Choose "Add FileMaker Data source" from the specify drop down.
Use this dialog to find and open the file hosted on your server by clicking the Remote button, just as though you were doing this by choosing Open from the file menu.
Click OK and save until you have left manage scripts.
Select File Options from the File Menu.
In here, you'll find you can set this file to perform a script automatically when the file opens. Specify it to perform the script you just created. In FileMaker 11 and older, you'll find a section labeled "when opening this file" that has a "perform script" check box to click to do this. In FileMaker 12, you'll click the "script triggers" tab and then select the OnFirstWindowOpen event.
Close and re-open this file and you should see it automatically open the hosted file on your network for you.
You can then copy this file to each computer on your network where you want this opener file.
(You can add a close window after the open file script step to close the opener file once it has opened the hosted database.)