Problem with that is the Russian visa restriction tend to make inward travel problematic
Ryanair do not need to and almost certainly would not want to act as the principal on any coach journey. The trick would be that Ryanair has a link on its website, pointing to a coach company that runs coaches between Tallinn airport and St Petersburg.
The coach company has a clear message on its website saying that if Estonian / Russian immigration don't like you, then you either don't get a refund or they'll put you on the next coach with a spare seat back to where you came from. Because they are a coach company rather than an airline, all the airline-specific legislation from the EU does not apply - i.e. no refunds, and the coach company does not get fined for bringing you across a border without a visa.
Ryanair would make money, a) by filling more seats on its flights, and b) the coach company paying a commission based on each ticket sold via the Ryanair weblink
One should of course consider, that processing a coach load of people at the EU-Russian border will take a substantial amount of time - there's always one person whose papers are complicated for which everyone else has to wait.
I have no idea whether this would actually generate worthwhile substantial income for either of the 2 companies