It looks like you should be able to with the HTTP API.
You could add the following Channel to the Thing (untested):
Type number : preset "Preset" [
commandTopic="wled/RGB2/api",
formatBeforePublish="PL=%s",
stateTopic="wled/RGB2/v",
transformationPattern="XPATH:/vs/ps/text()"
]
Link that to a Number Item, and if using a Sitemap set the mappings
appropriately.
I don’t use presets, so can’t test this.