You certainly could, although in my climate it is recommended that tree mallow be pruned back hard each year in early spring. While the plant grows huge (and very rapidly at that), the stems really don't ripen into a real woody framework so the plant can be quite floppy and stems liable to break or split. I would think this is even more likely to happen if it was carrying the weight of a vine. In a hotter climate like yours, this may not be the case.

btw, Lavatera is not considered a very long lived plant - about 5 years or so, so that might be another issue to keep in mind.

Thanks Gardengal! I hadn't even considered that the lavatera might not be around for much longer! I probably don't prune it hard enough either.... Good things to consider. Thanks for the thoughts.