[BioC] using nlme correlation structures in limma?

[Jacob Michaelson]

Do any of the BioC demi-gods know how difficult it would be to use  
nlme's correlation structures:

corAR1
autoregressive process of order 1.
corARMA
autoregressive moving average process, with arbitrary orders for the  
autoregressive and moving average components.
corCAR1
continuous autoregressive process (AR(1) process for a continuous  
time covariate).
corCompSymm
compound symmetry structure corresponding to a constant correlation.

...in limma's lmFit as the "correlation=" argument?

Thanks in advance,

Jake