You could try to tweak the default idle timeout value if it helps you.
Try following in terminal window

gconftool-2 -s /system/osso/connectivity/network_type/default_idle_timeout -t int 300

The value 300 means 5 minutes. Default value is 60. Note that the value is used also in powersave mode so you might not want to increase the timeout too long. Note also that there is no system UI for tweaking the value.