I just made some color flow plagues. I need to use a popsicle stick on 2 of them. How can I glue the stick to the plagues without using royal icing. I don't want to make a batch of royal icing just for this.

melted chocolate or you could probably use more colorflow if that's easier to mix.

Melted choc is probably your best best since yhou don't want to make any more colorflow.
One other option would be to mix a bit of powdered sugar & meringue powder if you have it (dry) now add a few drops of water until it is a thick mud. This will dry just a hard as actually making colorflow.

candy melts will work if you want just a spot of it to use as glue.