Time-based cryptanalysis: How to defeat it?

[anonymous-remailer at shell.portal.com]

Assuming Alice is decrypting a secret message sent to her
by Bob (on her very slow C64 ;), and Mallet is watching
with a stopwatch in hand, hoping to determine Alice's secret
key...

It would be good to place inside the decryption routines
a timer (WELL PLACED!) that waits a random-number of cycles
(based on key-strokes, mouse position, etc.) to defeat this
type of cryptanalysis?