You can use a private.xml like this with Karabiner (previously named KeyRemap4MacBook):
<?xml version="1.0"?>
<root>
<item>
<name>test</name>
<identifier>test</identifier>
<autogen>__KeyToKey__ KeyCode::F13, KeyCode::BRACKET_LEFT, VK_SHIFT</autogen>
<autogen>__KeyToKey__ KeyCode::F14, KeyCode::BRACKET_RIGHT, VK_SHIFT</autogen>
<autogen>__KeyToKey__ KeyCode::F15, KeyCode::BRACKET_LEFT</autogen>
<autogen>__KeyToKey__ KeyCode::F16, KeyCode::BRACKET_RIGHT</autogen>
</item>
</root>
Change for example KeyCode::BRACKET_LEFT, VK_SHIFT
to whatever key combination inserts {
in your keyboard layout.