You need to add your custom path in openerp-server.conf  file

for example in linux server the file usually reside in /etc directory, edit and  look for the following line 

addons_path = /opt/openerp/server/openerp/addons

to add custom path 

addons_path = /opt/openerp/server/openerp/addons,custom_path_here

As for window goto the installed folder

for example:

C:\Program Files (x86)\OpenERP 7.0\Server\server

look for the openerp-server.conf file and do the similar, make sure you have administartor previledge to edit the file.