There is no simple way to do this without sysadmin I am afraid,, its a design flaw in SQL, but an intended one. There is a connect item about this, perhaps you would like to vote on it -

https://connect.microsoft.com/SQLServer/feedback/details/156852/sql2005-sqlagent-msdb-security-roles#tabs/

what I have done in the past is set up a SQL account to be used by a group of people and they had to use this account to maintain their jobs. the exact rights you would need to give it would depend on what the jobs did.

dbcreator role possibly

EXECUTE on master.dbo.xp_sqlagent_enum_jobs

add the user to msdb

add to role SQLAgentOperatorRole

grant the account rights to use the proxy (execute sp_grant_login_to_proxy)

grant select on msdb.dbo.sysproxies

grant SELECT on msdb.dbo.sysjobs

grant select on msdb.dbo.sysjobs_view

grant select on msdb.dbo.syscategories

this was in a dev environment rather than production