There only is the hard way of copying your process (via fork), patching up your scalar like your OS would, and then jumping (via XS or assembly code) to the start of the process.

On Solaris, the /tmp "directory" resides in RAM and is not flushed to disk - if it really is a pressing matter of performance, you could mount /tmp as a ramdisk on your system as well. Note that for security reasons, programs in /tmp often are not allowed to execute, because malicious code uses this directory as a vector to drop files. So you might want to set up a directory similar but different from /tmp.