r - How to get confidence interval for hypothesis test of non-linear multiple parameters

Question

I am trying to do something that seems very simple yet I cannot find any good advice out there. I would like to get the confidence interval for the non-linear combination of two coefficients in a regression model. I cam use linearHypothesis() to conduct an F-test and get the p-value for a linear combination. The code I ran for that part is:

reg4 <- lm(bpsys ~ current_tobac + male + wtlb + age, data=NAMCS2010)
linearHypothesis(reg4, "current_tobac + male = 0")

I can use glht() from the multcomp package to get the confidence interval for a linear combination of parameters:

   confcm <- summary(glht(reg4, linfct = c("current_tobac + male = 0")))
   confint(confcm)

But I'm not sure what to do for a non-linear combination like (summary(reg4)$coefficients[2])/ (summary(reg4)$coefficients[4])

Any advice?