Weak instant gas boiler needs boost!

[Scatch]

Can you tell me if it's feasible to boost the output of a small instant gas boiler fitted in our mobile home? The water runs hot enough just at a very low flow rate and the bolier's running on full for temperature. If I increase the flow rate the temperature drops to an unusable degree. I thought that if we fitted a secondary electric heater unit in-line this might send the water into the boiler warmer thereby solving the problem. Is this do-able?