Open Terminal, and type this command to list all partitions on your hard drive or SSD:
Identify the "Recovery HD." For example:
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *120.0 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS Filesystem 119.2 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
Then run the following (replacing [ID] with your identifier (will most often be disk0s3).
diskutil mount readOnly /dev/[ID]
So the following would look like:
diskutil mount readOnly /dev/disk0s3
The disk image inside the Recovery HD partition has been marked invisible, so use the Terminal command to mount it:
hdiutil attach /Volumes/Recovery HD/com.apple.recovery.boot/BaseSystem.dmg
Now, from the newly mounted Mac OS X Base System Image, double-click the 'Install Mac OS X' application and proceed past the licensing agreement.
Choose the external drive or spare partition when the installer asks where you'd like to install OS X Lion.
Once the installer completes the download, do not restart your system. Rather, quit the installer. If you restart, you'll likely lose the local Lion installer. Once you have the InstallESD.dmg in the Mac OS X Install Data folder, you can burn it to a DVD, or image it to a USB flash drive to create your very own Lion boot disk.