Second SIM card

Hi I currently have a Smarty SIM card in a MIFI unit that I use in the summer months. I have decided to fit a fixed router with external aerial and need a full size SIM card, which I have purchased. As I have tried to activate it my email address flags up that I am a current Smarty customer so when I click on the "log on" it takes me to my previous account.

The new SIM card will be inserted in a router and fixed in such a way as to be difficult to access so I want to test it before fitting in about 10 days time. I need to activate the sim and want all correspondence to be sent to my email address as the routers and wifi  units don't have telephone numbers. I cannot do this as the activation process keeps taking me back to the original account which I will keep but only use in the summer months.

Any idea how to go about this. I probably won't want both in operation at the same time. but want the flexibility to do so if needed