NFS shares and umask

I have a directory on the server, shared by NFS. When I create a file there (through NFS), it has the default rights: 755. I want all the files I create on that share to have the rights: 775 (so that other members of the group can write them). Is there some place I can specify a umask for that share? -- GPG fingerprint = 3D45 5509 D380 26A4 523E A9D8 A66A 5F38 CA43 BB0E