Dear McCork,
you are confusing the issue by perhaps using an incorrect/improper definition for the term "optional".
In the context of the Council of Trent's Session VII, On Baptism, CANON V. :
"-If any one saith, that baptism is optional, that is, not necessary unto salvation; let him be anathema. "
Optional here does not mean "possible but not compulsory; left to personal choice", instead it would be correctly translated as "free, superflous, unnecessary" as other translations and the latin text make clear:
6. "Si quis dixerit baptismum liberum esse hoc est non necessarium ad salutem: anathema sit."
The necessity regards the Sacrament itself, not the person's obligation and/or potential possibility of choice, preference, will.
Therefore, if we were to accept BOD as usually understood, even by you, it is true it would be optional, ergo unnecessary, superflous, free.
Understood in a strict and Catholic way, it would not be optional, as the Sacrament itself would be administered via the desire, and it could only ever apply to those who, for some reason (hypothetically but dubiously) were unable to obtain the actual physical Sacrament while wanting to (having explicit desire for it).
Having said that, in the usual BODomaniac understanding of "baptism of desire", I would venture out and say it truly is optional even in the sense you erroneously meant, in fact.
One could actually delay the Sacrament, being aware of BOD, as even the desire for the Sacrament is wholly unnecessary, only thing required is an implicit will to conform to an implicit understanding of one's faith.
Unless you can somehow demonstrate that BODomaniac's BOD would not apply to someone willingly delaying the Sacrament due to his reliance on BOD itself.