Pt-archiver --columns with alias

Polyglot Projects Percona Toolkit
1

I need to export a given value which is extracted with a call to a function. Like so:

SELECT getCountry(md) as geo FROM table

It seems that --columns 'getCountry(md) as geo' does not work

DBD::mysql::st execute failed: Unknown column ''getCountry(md) as geo' in 'field list'

Any workaround ?

Thanks,
Luis