Ask any Traditional Catholic priest and he'll tell you the same thing. You are NOT bound by this oath, and in fact have an obligation to BREAK the oath, just as you would have an obligation to break your oath to murder someone. Simply confess the fact that you made this oath in the first place, but other than that there's absolutely nothing to this oath.
Last Sunday I did exactly as you recommended and I said that I would.
1. My
dioceses parish priest told me not to worry, all was ok and I did not need to confess as no sin was committed and I was free to keep or not the promise as only God would judge my actions.
2. My
SSPX priest:
(i) it is a
sin (*) and I should confess it. The sin hurts Jesus, under three counts:
a)
pride (I have such a high esteem of myself that I think that I can decide on matters of souls);
b)
sloth (I was too lazy to fight the battle to save my wife's soul);
c) venial sin of
weakness, because I gave up.
(ii) the
promise is null because there was a defect of will on two counts and a defect of capacity.
Defect of will, firstly, because of my ignorance concerning souls caused me to err believing that I could make such a promise, in the first place. The second count was on force majeur: I resisted for three years and I would not have created a family and conceived a daughter that I would raise in the Catholic Faith, as I then also insisted for.
There was a also a
defect of capacity: I was unable to enter into the contract of evil deed as God rejects prayers for evil.
(iii) the Catholic
marriage will remain valid even if the Orthodox permission should be revoked, because our Church does not recognize the authority of other religions over the sacraments.
My priest reduced my penance considering that the sin was SUBJECTIVELY mitigated by the fact that I committed it in good faith (ignorance) and for a good cause (creating a Catholic Family).
The funny part of the incident was that when I told my wife (who came a second time to Mass) she joked about it: "You men always need someone else to tell you what to do..."
(*) but for a different reason. Not because I am obliged to pray for her conversion, as you suggested, but because it is not charitable to not try to save someone you love (he made the example of watching a loved one being run over by a car and not rushing to pull him away).