I introduced the Demi-Creator Postulate (DCP) here. This post explores the concept further.
Young-earth creationism (YEC) accepts what might be called the Biblical Creator Postulate (BCP). This postulate is an attempt to bring the Creator as described in the Bible into science. Not only does this bring theological debates into science but it also makes scientists attempt to determine what the Creator should be expected to do that could be observed, which makes scientists into theologians. This is science as practiced in the Middles Ages, when the Roman Catholic Church’s status in Europe ensured theological conformity. The Reformation and the Scientific Revolution have prevented such a situation since the 16th century.
In contrast, a demi-creator (DC) is a hypothetical being definable for the needs of science and observable only indirectly. Whether or not a demi-creator is a window on the Creator of the theologians is a metaphysical question, and so not a concern of science.
I would initially describe a demi-creator as a master designer and builder, who meets their given design criteria, whether these criteria are unknown to us or are specified in a separate postulate. This demi-creator is like us in their intelligence and reasoning ability, only greater and with the ability to produce an extremely complex design that works. This enables us to make inferences about what to expect they have done given what has been observed.
The DCP enables science to consider the possibility of a creator without going outside of science. It posits more than the intelligent design (ID) proponents have been willing to admit but less than what is assumed by the YECs with their BCP.
Addendum (12/2018): The DCP could perhaps better be called the Designer and Builder Postulate (DBP). Intelligent design implicates a designer, and there must also be a builder to implement the design. This designer and builder is not necessarily a creator in the sense of creatio ex nihilo. What is necessary is that the design should be intelligible to us and that the making should be possible.