ei.cfg

http://jerryching.no-ip.org/Software/ISO%20Backup/Windows%207/

http://176.99.4.36/Windows%207/Eng/

http://www.farstone.com/bootablemedia/index.php

Modify the ei.cfg using your choices to set the desired edition, channel and volume license flag.

ei.cfg looks like this:
[EditionID]
Ultimate
[Channel]
Retail
[VL]
0

Choose the edition for the ei.cfg:
Ultimate
Professional
HomePremium
HomeBasic
Starter

Choose the channel for the ei.cfg:
Retail
OEM
VOL

x86:
cdimage -u2 -udfver102 -b<windows 7 files path>\boot\etfsboot.com -o -lGRMC<edition_code><channel_code>_<language_code>_DVD -t<file_date>,<file_time><windows_7_files_path><new_file_name.iso>

x64:
cdimage -u2 -udfver102 -bootdata:2#p0,b<windows_7_files_path>\boot\etfsboot.com#pEF,eb<windows_7_files_path>\efi\microsoft\boot\efisys.bin -o -lGRMC<edition_code>X<channel_code>_<language_code>_DVD -t<file_date>,<file_time><windows_7_files_path><new_file_name.iso>

Options:
File Date: July, 14 2009
File Time: 02:26:40
Edition codes: ST (Starter), HB (Home Basic), HP (Home Premium), PR (Professional), UL (Ultimate)
Channel codes: FRER (Retail), FREO (OEM), VOL (volume license)
Some language codes: EN (English-USA), FR (French), DE (German), IT (Italian), ES (Spanish)

For example, Professional ISO:

Using the ei.cfg:
[EditionID]
Professional
[Channel]
Retail
[VL]
0

Path: Windows7
File Date: July, 14 2009
File Time: 02:26:40
Edition: Professional
Channel: Retail
Language: English-USA

CDImage settings (x86):
cdimage -u2 -udfver102 -bWindows7\boot\etfsboot.com -o -lGRMCPRFRER_EN_DVD -t07/14/2009,02:26:40 Windows7 win7_professional_english_x86_retail_official.iso

CDImage Settings (x64):
cdimage -u2 -udfver102 -bootdata:2#p0,bWindows7\boot\etfsboot.com#pEF,ebWindows7\efi\microsoft\boot\efisys.bin -o -lGRMCPRXFRER_EN_DVD -t07/14/2009,02:26:40 Windows7 win7_professional_english_x64_retail_official.iso