Iterative refinement algorithm for computing exp(x) with arbitrary precision
Solution 1:
There is an algorithm for computing $\log_2(x)$ that might suit you. Combine that with the spigot algorithm for $e$, and you can get $\ln(x)$. From there, you can use Newton-Raphson to get $\exp(x)$.
I don't know if this roundabout way ends up doing any better than just recomputing.