I know struts2 but not struts1 (so these solutions attack from that angle, a struts1 person may have a much prettier solution with respect to this issue):
1) Add Spring (if it isn't there already)... add those methods using AOP. [cost: possibly learning a new technology]
2) Use Struts2 beside Struts1 mapping .action to struts2 and .do to struts1... create a struts2 package, possibly called "token" and possibly mapped to /token with appropriate actions with wild cards to capture what ever you throw at it... which forwards to the struts1 actions. PS: You asked how it could be done... this is far from pretty and I wouldn't do this. [cost: complicates mapping logic ]
3) Convert everything to struts2 and use the token interceptor. [cost: high time investment]
4) Create a new base action class which your actions will extend, implementing those methods.