You can anchor wires at the base of your trellis for Clematis if the wood doesn't allow them to cling. Just place a rock or brick at the base of the arbor and run the wire around the rock , then up to where you want the Clematis to run. You can have a few wires with this method if you have enough stems on the Clematis. The wire is hardly visible.

Clematis does not self attach. It can only "climb" by twining around something of relatively small diameter, like wire mesh, mono filament fishing line or lattice. This is true of all clematis. You can plant a clematis on a solid wood wall if you also attach something to the existing wall that will meet its needs.

Climbing hydrangeas use aerial rootlets generated by the vine to attach to and climb porous surfaces like unfinished wood, stone, or brick. In the absence of a porous vertical surface, a climbing hydrangea becomes a mounding shrub.

What perplexes me is your reference to Silver Lace vine. It is also a twiner. What is it twining around to climb the lower part of the wall? Is it twining around another vine? Is the wall solid wood at the bottom or are there spaces between the boards?