Conditional imports are less

I've tried two ways to do additional imports, but neither works. Is this at least 2.6.0 possible?

@useRTL: true;

& when (@useRTL = true) {
    @import "bi-app/bi-app-rtl.less";
}

@useRTLpath: "bi-app/bi-app-rtl.less";
@import (optional) "@{useRTLpath}";