Excel for RT doesn't support addons no, bit silly really as the .NET based addons would function fine on the ARM platform without alteration.
Only option left would be open office and its plugins. But open office for RT has not been done and is incredibly complex so might never be done, especially as the majority opinion last time it was discussed was that the effort wasn't worth it when most office users don't even use plugins or macros and can use office for RT fine so it would be a wasted porting effort for perhaps a handful of people. Not to mention that open office plugins are platform dependent so any plugins required would also need to be redone for RT. Ultimately this option is out.
I would look into whether you can get away without the data analysis package. If you can't, then sorry man, your out of luck.