Involving stakeholders in requirements elicitation is a cornerstone of successful requirements engineering (RE). With the recent technological advances, the number of stakeholders of a system has significantly increased. Major stakeholders, end-users in particular, are increasingly difficult to reach, because they may be globally distributed and outside organizational reach, i.e., they are no members of the organizations that are involved in the development of a system. Online elicitation platforms allow to elicit requirements collaboratively from a large number of distributed stakeholders. However, such platforms are not sufficient for motivating stakeholders outside organizational reach to contribute voluntarily. Gamification is a potential means for creating and sustaining such motivation. However, there is little research on stakeholder engagement with gamification so far. Current approaches particularly do not consider that stakeholders learn during elicitation and that their motivational factors also change. In this paper, we address this gap with a motivation concept that is inspired by the theories of experiential learning and need satisfaction. Our contribution is threefold. First, we suggest how to characterize these stakeholders despite not knowing who they are. Second, we show the role of experiential learning and need satisfaction with respect to gamification in the context of requirements elicitation. Third, we present a three-dimensional concept of how to motivate these stakeholders towards requirements elicitation over the whole period of requirements elicitation.