nls, nlrq, and box-cox transformation

Dear r-help members
I posted this message already yesterday, but don't know whether it
reached you since I joined the group only yesterday.
I would like to estimate the boxcox transformed model
(y^t - 1)/t ~ b0 + b1 * x.
Unfortunately, R returns with an error message when I try to
perform this with the call
nls( I((y^t - 1)/t) ~ I(b0 + b1*x),
start = c(t=1,b0=0,b1=0), data = mydataframe)

The error message is:  Object "t" not found

Apparently R seems not to accept parameters on the left hand
side of a regression model. I know that my do-it-yourself
strategy is not necessary, since the package box-cox is
available. Unfortunately, I want the use the box-cox
transformation in a quantile regression, i.e. I have to replace
nls by nlrq in the call above.

Any suggestions?

Thanks and best regards,
Johannes Ludsteck