how much higher can i go in current ripple RMS
None, of course, at least if you want to rely on anything else the datasheet says.
The heating is a function of the RMS current. No, you don't get to cheat physics. Calculate the RMS of the pulse waveform, and make sure that doesn't exceed what the capacitor can handle.
Note also that there may be other limits, like short term pulse current, instantaneous voltage, and possibly maximum allowed heating over a short time window. The RMS of your pulse may be within spec, but it may violate one or more other such parameters.
As always, you have to read the datasheet carefully and make sure you take all the limits into account.