You might have to email them to ask them to put your operating system on the SSD then. I'm not sure how they handle that. Jenny posted a link on how to point your data to the HDD, but I don't remember what it was. I'm away from home now in NW Iowa, so am not at my computer.
If you get the bigger SSD, you can always put a few of your most used programs there too.
In my PC corner for the winter, gaming, knitting and reading.