Gnome - Main menu, Freemind, How to add java memory-settings to an existing entry?

Question

I have installed Freemind in Gnome. And the entry in the main menu is "freemind %U".

Freemind works fine but when I try to export a map to PDF, the resulting PDF can not be opened and the freemind application itself can only be stopped with the kill-command.

Browsing on internet, I saw that this could be solved by changing the Java memory-settings.

I have two questions:

1. What settings should I use?
2. How can I add those settings to the entry in the main menu?

Ben