I would stake the tree a couple of years, some people use small weights hung on a twine. I've done by wood pieces with V notch on ends, one end goes on top of branch being pushed down, other end is going onto the stem wedged under another branch.
Also done by your idea, pull towards the ground with a elastic string onto a stake in the ground,..but the tree should be staked when doing it like this.

could try toothpicks or cloths pins. Just clip one branch, so the small branch is in the gap, then put the other end on the trunk.

If your branches can't be spread with a toothpick or CP and trees are so small maybe these are oversized branches to begin with. They should never exceed half the diameter of the trunk at the point they are attached to it, except as one strategy for developing an open center tree (even for this there are advantages to less dominating branches being used).

Oversized branches don't usually lose excessive vigor by simply spreading them as relative diameter determines relative access to N and water, as well as stored carbos from the roots (I recently learned of the stored carbo part).

The apple tree, for example, has 4 grafts on the rootstock; I'd like to push each out so that they grow out rather than just up and out. Two of the branches aren't going to bend, but 2 will.

I'll look at the CP trick but I'm not sure there is a point where the CP can be connected to the branch AND wedged against something else.

Andrew