Does your external enclosure have two Thunderbolt ports? I have multiple TB LaCie drive connected but all have two TB ports and I use them between my Macbook Pro and my Thunderbolt Display (the display should always be at the end of the chain).
I really don't think that, if your enclosure has only one TB port, that you're going to be able to do what you want. You may want to look into an enclosure that has two Thunderbolt ports.
I believe it'll work too, since Apple says the display is a fully compatible hub... but still, that's kinda risky (1.000 €).
No, my "enclosure" is a Seagate GoFlex with only one TB port (2.5" version).
Anyway guys, if it goes wrong I will take the mini in and put the SSD inside.
Thanks for your help!