I don't know, but I thougt in the Lambert function
If we define [tex]x^x=z[/tex], then, x=[tex]\frac{ln(z)}{W(ln(z)}[/tex], where W is the Lambert function. So we can write
[tex]x^z=\left(\frac{ln(z)}{W(ln(z)}\right)^z[/tex], and then integrate.
I know, that this is awfull, but, maybe it can help or give any clue.