[R] How to remove outer box from Wireframe plots?

[Seth W Bigelow]

I would like to remove the outermost box from my wireframe plots -- this is
the box that is automatically generated, and is not the inner cube that
frames the data. There was a thread on this 4 yrs ago but none of the fixes
work (e.g., grid.newpage(), grid.lines(gp = gpar(col = NA)) or
par.box=list(col=1),col=NA. These just make the data or the cube disappear.
Has anyone solved this issue?
Here's some sample code. In case you are wondering, I have indeed purchased
Paul Murrel's book.

library(lattice)
library(grid)

w <- expand.grid(X1 = seq(-29.5,-25,0.1), X3 = seq(1,90,1))
w$z <- model(99.6,3.59,8.65,w$X1,0.5,w$X3)

wireframe(z~X3*X1,w,
 scales=list(arrows=FALSE))

Appreciatively,
Seth
Dr. Seth  W. Bigelow
Biologist, Sierra Nevada Research Center