Conditional variable in input string

Hello,

I'd like to use variable with condition for the date dimention in fuction setFilterExt.

Without condition it works fine. For example:

var Period = '09.03.2015';
DS_1.setFilterExt("ZPROBDATE", Period);

But it seems impossible to use variable with condition in input string:

var Period = '09.03.2015';
DS_1.setFilterExt("ZPROBDATE", '>=Period');

Did i miss something or is this a topic for an idea place?

As a wolkaroud i can use condition variable in BEx, but for me it would be more comfortable to set this filter in Script.