First off, we have to rewrite your 'base' present-tense sentence:
It will be foolish of him if he does not seize the opportunity.
This sentence is only marginally idiomatic as it stands, and it will not bear casting into what you call "impossible" modality. It's not really a conditional at all: the "it" which is to be "foolish of him" is neither a logical nor a practical consequence of his failure to seize the opportunity, it is the failure itself. We would ordinarily express this with an infinitival rather than a conditional:
It will be foolish of him not to seize the opportunity.
Moreover, the verb in the main (consequence) clause is a stative, so it cannot ordinarily be cast into the continuous construction.
So let's start by writing a true present-tense conditional with a continuous construction in the consequence clause:
If he thinks we will help he is deceiving himself.
This may be cast into present-tense "impossible" modality like this:
If he thought we would help, he would be deceiving himself.
And that may be cast into the past tense like this:
If he had thought we would help, he would have been deceiving himself.
That's probably what you have in mind when you speak of a main clause in "present perfect continuous" and a condition clause in "past perfect". However, those are not accurate descriptions of the constructions in these sentences. The apparent perfects are actually past-tense markers. He had thought looks like a past perfect, but it is actually an irrealis ("impossible") past; and he would have been deceiving looks like a modal present perfect, but it's actual a modal past.