I was going to suggest Acetone but according to Loctite that may not work. Heat may be the answer say holding a soldering iron tip on the bolt head:
"No solvent will wick into the joint to break the threadlocker down. This is either hand-tool removable at room temperature; if not, it requires high temperatures of 450-600°F (212-316°C) to separate parts. The products are thermoset plastics in the cured state that soften at higher temperatures. Thus, you need to disassemble while at the higher softening-point temperature. Do not let it cool down first. Otherwise, it will resoldify. Solvents like methyl ethyl keytone and methylene chloride can be used for clean up of residue only after disassembly."