So my friend for whom I'm doing a wedding cake has changed her mind on the design, she wants to add another tier. Which all around is no big deal - except for the sps system. I've already ordered it. I have enough pillars, but not the plate for the extra tier. There is nowhere local to buy it. This will be my first time using it sp I have no clue - is there any workable substitute for having to order (&pay another shipping charge) on the one extra plate I need?

I'm not sure. Leahs could probably tell you if there's anything that you can do. Honestly, I would probably just tell your friend that you need to order the extra stuff and that she's going to have to pay the extra shipping since it's late in the game. Hope this helps!

When there is no other way a good sub for SPS is Wilton's hidden pillars & one plate (that the cake will sit on). It is very, very similar.

Can somebody pls explain what an "SPS" system is? tia

There is a tutorial by Leahs in the "How Do I" forum secton. It's a "sticky" at the top of the forum. Here's the link. It has pictures and a great explanation. Basically, it's a really good support system for your cake. SPS stands for single plate separator. Just download the tutorial and you'll be on your way!!