Sharepoint 2010 - Make assigning users easier

we are using Sharepoint 2010 and maintaining an Action Item/Issue tracker list (for a limited number of people, <10). To make assigning Action Items to users easier I want to implement to option to either click on checkboxes

[ ] Jan [ ] Chris [ ] Sara

to select to whom to assign this task or to use the Sharepoint lookup and maintain a list of users (with 2 rows, one row saying Jan and the other one containing the link to this person) tasks can be assigned to in a seperate list (better option in my opinion).

I then want to use a Workflow to map the list with names to the real "Assigned to" field shown in the Action Item entry. This is where I'm currently stuck, I tried various options but they all don't work because I cannot do String modifications.

Anyone has a solution how to implement this?

Thanks and BR Orbit.