So you have to do some research to make this possible, and I'd like to share how I did.
I found out two links are useful to follow: link1 and link2. You may need Dell account to access link2. Belows are brief steps.
1. Update to Windows 8.1. You may need to update fully to see the Windows 8.1 update in the app store. Especially KB 2871389 and KB 2917499 should be updated before you try to find the Windows 8.1 update. Please see the link to troubleshoot this.
2. Install mSATA drive. Please see my previous blog for this.
3. Format the mSATA drive without partitions.
4. Clone the windows active partition to mSATA. You may want to clone all partitions to enable Factory recovery with the mSATA SSD, or you just can clone windows parition (C drive) to make partitions simple. I used Macrium Reflect Free to do this. If you want to clone all partitions, you need to drag and drop each partitions when you designate partitions to be cloned.
5. Reboot and enter to BIOS (holding F2 before Dell logo appears). Change SATA Operation from “Intel Smart Response Technology” to AHCI, Save settings and restart.
6. Reboot and you may start your system from an original HDD. Use Visual BCD 0.93 to change boot order. The above link2 said you need not to use EasyBCD 2.2 to avoid any troubles. I used Visual BCD 0.93 to change the boot order. Select Windows 8 in the loaders section. Change the two entries that has C: to D: (whatever where the cloned Windows system exists).
7. That's all. You can now see fast booting of Windows 8.1.