It is as if the preposition is reinterpreted as part of the stem. Smyth lists some examples in sections 449-454 of his grammar.
The challenge is how to model this in FLEx and stick with traditional citation forms for the verbs. I don't know if FLEx would allow a complex form consisting of a proclitic and verb stem (e.g. ana= blep). If we could combine such a lexeme form with a citation form anablepoo (ἀναβλέπω), then we might have an elegant and easily implemented solution. (The equivalent in English is our phrasal verbs, which we treat as a kind of idiom.)
Kevin has given the other option--treating these affixes as prefixing interfixes.
Unfortunately grammar has its irregularities. For instance aphijmi 'allow, forgive' (ἀφίημι from ἀπό= ἀφίημι) can prefix the past tense both ways:
ἤφιεν 'he was allowing'
ἐ- ἀπό= Cι- ἑ -ν
PST- from= IPFV- let -3S
ἀφῆκεν 'he allowed'
ἀπό= ἐ- ἑ -κε -ν
from= PST- let -AOR -3S
Since ἐ- and Cι- are both prefixing interfixes, the form ἤφιεν tries to have it both ways, prefix and prefixing interfix. (Perhaps calling them "interfering imperfixes" would better express how I feel about them.) Probably one or both of these forms will have to be treated as irregularly inflected forms.
By the way, I'm working on a new Greek lexicon of New Testament Greek. The project is on LanguageDepot (Greek-SBL). Let me know if you are interested in downloading it.