Official Ruling
No, you can't. A "by" condition can't be met if only some of the required actions are performed. In order for the conditions for this card's {Hand} [Main] effect to be met, you must pay 3 cost and place this card as the bottom digivolution card of your [King Drasil_7D6] or [Mother Eater] in the breeding area.
Source: BT23-072 King Drasil_7D6