One option is to have SQL Server Agent Jobs set up to run the SSIS packages, but don't schedule the jobs to run automatically, and then have a web application or other front-end app that you are building start the relevant job using the sp_start_job stored procedure in the msdb database. You will need to grant permissions to whatever security account you are using to execute this procedure. I've done this before by granting the login membership of the SQLAgentOperatorRole in msdb. You might then want to build in some sort of mechanism to poll the execution status and history of the job to display in your GUI.