dynamic date calculation in variants: set First day of current month + X days

Hi, I need to set variable date in Date range selection field of a variant. It should be from first day of current month + X days, till First day of next month + X.

With 'D:Dynamic dates calculation' I see following options: Current Date. From month start to today. Current date +/- ??? days. current date +/- ??? work days. First day of current month. nth working day of current month. First day of next month. First day of previous mont. Last day of previous month. Last Day of the Current Month. First quarter ????. Second quarter ????. Third quarter ????. Fourth quarter ????. Current date - xxx,current date + yyy. Date - xxx, Date + yyy (work days). Previous month. Current period (Beginning of mth-xx months, end of mth+yy months).

So, any options fits exactly to our requirement. Is there a way to achieve this? Not sure how table TVARVC works, and if that specific selection options could be configured via STVARV