What kind of plants do you have?
Some plants as they grow send out roots further up the stem, if you have any plants that do this - I have planted mine lengthways in the substrate with just the leaves sticking above ground level. This way , many small plantletts started growing and had a good anchor to hold them in place while theier big roots grew.
If you have small rooted plants, how about attaching them to wood, or a large pebble and then planting the pebble under your substrate.