Do you mean a CPU with lots surface area for the glue? Because I'd really worry about gluing a big ol' HSF to just the tiny center square of an Athlon.
OTOH I've glued HSFs to K6 and old 466 MHz Celerons with just silicone rubber sealer. It sticks and cools better than thermal tape, and silicone rubber sheets are used for cooling transistors inside PSUs. But if you don't like it, it's so soft that you can just slice through it with a razor. I use it to glue tiny heatsinks to lots of voltage regulators on mobos.
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