You must have the feat to fulfill the feat prerequisite
General rules support
The section "Reading the Rules" that explains the elements of a rules stat block says:
Prerequisites Any minimum ability scores, feats, proficiency ranks, or other prerequisites you must have before you can access this rule element are listed here.
This states you must have the feat in question. Shield block says that you do not have the feat, so it does not qualify.
Optional support: Inference through rules consistency
The "usual language" you refer to presents an actual rule:
Since this proficiency is temporary, you can’t use it as a prerequisite for a skill increase or a permanent character option like a feat
It tells you that if a profieciency is temporary, you cannot use is as a prerequiste for a feat. That this reminder text is repeated for many features instead of just being cited once in a general rules section does not change its core statement: temporary proficiencies cannot be used as prerequisites.
It would be different if it just said: "This proficiency cannot be used as a prerequisite for a skill increase or a permanent character option like a feat". In that case, it might just apply to the feature in question.
But it does not say just that. It gives you a reason why: because the proficiency is temporary. If that is the reason, the same reason applies to any temporary proficiency.
Now, @KRyan pointed out in the comments that historically, Pathfinder has a heritage of being an "exception-based" ruleset. I was unable to find anything that directly explains this in the same way as, for example, the rules for D&D 3.5 do which explicitly say that the rules are applied general to specific to exception in increasing order of precedence. The closest I found was under "Reading the Rules"
This book contains hundreds of rules elements that give characters new and interesting ways to respond to situations in the game. All characters can use the basic actions found in Chapter 9, but an individual character often has special rules that allow them to do things most other characters can’t. Most of these options are feats, which are gained by making certain choices at character creation or when a character advances in level.
The idea here would be that these special rules may not apply in general, because they are tied to the specific special option. However, for the game to handle things consistently. If you follow that logic, nothing that is written in a specific feature can be used to derive general rules.
While that may be legitimate, I think that in the absence of straightforward, general rules, looking at specific examples of something is a valid approach to try and understand how the game handles that something, especially if there is a very high degree of consistency and repetition for that something, like in this case.
However, in this case, it is not needed, because there is a general rule that is also straightforward to apply.