gDevilspie can do that for you!
What is gDevilspie?
A user friendly interface to the Devil's Pie window matching daemon, To create rules easily.
Devil's Pie is a window-matching utility, It can be configured to detect windows as they are created, And match the window to a set of rules. If the window matches the rules, it can perform a series of actions on that window.
How to install gDevilspie?
Hit Alt+Ctrl+T to open terminal and run following command:
sudo apt-get install gdevilspie
Or search for gDevilspie
in Software Center and install from there.
How to use?
- Once installed, Hit Super key (Windows key) to open Unity dash and search for "gDevilspie" and open it.
- Open "Gimp".
In gDevilspie click on "add" to add a new rule.
In "Rule Editor" Click on "Get", Select Gimp window and "Apply".

- Name this new rule as "Gimp" in top field.
- Under "Matching" tab enable "window_xid" and "application_name"

- Under "Actions" tab enable "maximize" and click save.

- On the main window enable the option "Start devilspie daemon automatically at login" and click on "Start". That's it!

Now whenever you will start "Gimp" it will automatically be maximized. You can add rules for "Update Manager" or any other program in the same way.