Keep EPG last 7 days

Hello, i want to know if this is possible or can someone add it in next update.

I need to have epg xml data for 15 days, past 7 days, present day & next 6 days.

Everytime i run web grab he overwrites guide.xml and starts grabbing from current day and does not keep any data from past.

Most of the ISP's have the past 7 days & next 7 days epg guide, why dont add an option like <timespan></timespan> to grabb past days?
For example:

<timespan>7</timespan> -> current day + 7 days

<oldtimespan>7</oldtimespan> current day - 7 days

This will grab last 7 days and next 7 days from site everytime we run webgrabber.