Replace original HD with 2 SSD's

Oh, sorry.

Yeah, that should be entirely possible.

Here's the iFixit guide for replacing the original HD:

Sostituzione del disco rigido nel Mac mini, versione metà 2011

In combination with the steps to instal the second hard drive, again located here:

Installazione dell'SSD Dual Drive nel Mac Mini, versione metà 2011

The final step of the second hard drive installation addresses the question of running the SSD as the primary. Specifically it says:

"To minimize the amount of work necessary when adding an SSD to be used as your primary drive, we recommend installing the SSD like we did in this guide and leaving the stock platter drive in its original bottom position (closest to the antenna plate). After reassembly, boot the Mini into Lion Recovery and use disk utility to erase your SSD. Then install Lion on your SSD. After rebooting, go into system preferences>startup disk and choose your SSD as the startup disk."

Then you should be made in the shade. Since the device can boot off the SSD as a primary then you don't need the other at all.

Once you have the system booting off the first SSD, then you can go back in and replace the original HD with your second SSD.

Though you will be required to install them in two waves. Put in the first and get it to successfully boot off of the SSD as the primary. Then go back in and install the second SSD by replacing the original HD.