Wrapping pandoc table column names in r markdown

I am creating a pandoc.table with long column name that I want to wrap so my table does not go off the pdf page. I know you can use split.tables, but that takes away the clarity of the table. Using split.cells doesn't seem to do anything, even when supplied as a vector.

---
  output : pdf_document
---

```{r,echo=FALSE, results="asis"}
library(pander)
mytab = data.frame(ReallySuperExtraLongColumnNameThatIWantToWrap=1:2, col2=2001:2002)
pandoc.table(mytab)
```