Installing Snow Leopard on external drive with newer iMac version

I have two computers running different types of OS X. One is an iMac with Mavericks (10.9.5) and the other is a Macbook Pro with Snow Leopard (10.6.x).

My Macbook Pro isn't working (HDD problem), so I have bought another HDD for it. I've tried to install Snow Leopard (CD) in my newer HDD connected via USB to my iMac (cause if I try to install via Macbook Pro, it stuck in Apple logo), but when I try to install SL on external HDD it shows: You can't use this version of the application "Install Mac OS X.app" with this version of OS.

Is there a way to bypass this message and install the OS on the external HDD?

Additional info

• Macbook Pro model: A1278 (EMC 2326*);

• iMac model: iMac is MB417XX/A (2009).

Both Macs support 10.6.6 (the MacBook Pro probably was delivered with a Snow Leopard 10.6.6 DVD) as well as any later system up to at least 10.10 and both contain a DVD-drive. The MacBook Pro's optical drive seems to be damaged or malfunctioning.

Without manipulating the innards of Mavericks you usually can't install an older system over a newer system even if you install it to another volume. To circumvent this restriction use another method:

Here is a straightforward guide how to clone the Snow Leopard DVD to a thumb drive, then boot a second Mac from the thumb drive and install the OS. You can use a modified guide to accomplish the same on your iMac without needing to manipulate your Mavericks system.

Format the external drive:

• Open Disk Utility and format the external drive.
• Click the Partition tab
• Under the Partition Layout header click on the 2 Partition option in the drop-down menu. One big partition and a second smaller one with at least 8 GB at the end. Use the options button to choose GUID partition table.
• Click the Format drop-down menu and select Mac OS Extended (Journaled).
• To format the external drive finally, click the Apply button in the lower right-hand corner of the Disk Utility window.

Restore the Snow Leopard DVD or a Disk Image:

• Locate a Snow Leopard disk image or DVD on the Mac
• If you're using a disk image, mount it to the desktop
• In the Disk Utility window, click the Restore tab in the external's drive's menu

In the center of the window you'll see two boxes: one labeled Source and another Destination.

• Drag-and-drop the second partition of the external drive into the Destination box
• Drag-and-drop the Mac OS X Install Drive disk into the Source box
• At the bottom right-hand corner of the screen and click the Restore button

Disk Utility will restore the OS X Install DVD or disk image to the external drive; this process may take anywhere from 20 minutes to an hour depending on how quick the Mac is.

After the process has finished quit Disk Utility and try to reboot the iMac to the external disk. If the reboot is successful disassemble the external drive and move the disk to the MacBook Pro.

Boot the MacBook Pro to the second partition and install Snow Leopard to the first partition of your MacBook Pro disk.

After installing and rebooting to the first partition, open Disk Utility remove the second partition and expand the first partition to the full size.

If you have a spare thumb drive with at least 8 GB you may use this one instead and follow the guide in the link.