The crofting rules are specifically there to keep land in active agricultural use, that is their raison d'etre.
Decrofting is usually only granted for very specific reasons (usually a house site as it is required before a bank will give a mortgage) and I can't think of any reason why they would (or should) be willing to allow a whole croft to be decrofted.
A 'natural meadow' does not sound terribly much like agriculture to me however if you were to do it under an agri environmental scheme that would possibly count. The best solution though would be to get 2 sheep. You don't need to be earning a living from agriculture, just making an effort, however small that effort is.
Having said all that whilst the CC does have the powers to sublet unused croft land they are glacially slow about doing anything about it and if they started the process you would have plenty time to get those 2 sheep before it got anywhere. They are highly unlikely to do anything if you live on the croft - their priority is crofts which are held by people who live so far away there is no prospect of them doing any crofting.
Although in my opinion they need to pull their fingers out and get a bit more heavy handed with a few more vacant crofts
