Right now you can put another select in front of the chain, and leave one port empty, and add an Allow Changes node to prevent unessery events from entering the resize node.
I agree with the solution suggested by Bodysoulspirit. But I suspect that unnecessary “get image size” node are triggered anyway in his schema, even when resizing is not required, every time a new frame reaches “Blend images” node. Probably “get image size” is much less computational requiring than “resize image” of course, but it’s possible to skip it also. Moreover, “resize image” also is always triggered whenever the new frame has different dimensions.
This way should improve the solution, triggering “get image size” and “resize” just when strictly required (caveat, not tested):