Wire them to the dip beam with a switch and one of these to reduce light output. http://www.ebay.co.uk/itm/Mini-In-L...ome_Garden_Lighting_Parts&hash=item43c60b4601
There handle up to 6 watts but there are various versions. They use a power chopping method to reduce light output so current draw is reduced when working at DRL output levels.
Wire another power feed from the main beam to bypass the dimmer. This will give full power when main beam is on. It will probably need a relay to avoid upsetting the canbus.
A look around suppliers of these dimmers will find a wiring diagram.